Kye Gomez commited on
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[DOCS] [LICENSE]
Browse files- README.md +91 -1
- docs/open_mythos.md +471 -0
README.md
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# OpenMythos
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## The Central Hypothesis
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The injection of `e` at every step is what prevents the model from drifting — it keeps the original input signal alive throughout the entire recurrence depth.
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---
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## Why This Explains Mythos
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- Reasoning with Latent Thoughts — On the Power of Looped Transformers: https://arxiv.org/abs/2502.17416
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- Training Large Language Models to Reason in a Continuous Latent Space: https://arxiv.org/abs/2412.06769
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- Relaxed Recursive Transformers — Effective Parameter Sharing with Layer-wise LoRA: https://arxiv.org/pdf/2410.20672
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# OpenMythos
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An open-source and theoretically grounded reconstruction of the Claude Mythos architecture, built from first principles using the available research literature.
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## Usage
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```python
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import torch
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from open_mythos.main import OpenMythos, MythosConfig
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attn_type = "mla" # or "gqa"
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base = {
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"vocab_size": 1000,
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"dim": 256,
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"n_heads": 8,
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"max_seq_len": 128,
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"max_loop_iters": 4,
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"prelude_layers": 1,
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"coda_layers": 1,
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"n_experts": 8,
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"n_shared_experts": 1,
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"n_experts_per_tok": 2,
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"expert_dim": 64,
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"lora_rank": 8,
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"attn_type": attn_type,
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}
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if attn_type == "gqa":
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cfg = MythosConfig(**base, n_kv_heads=2)
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else:
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cfg = MythosConfig(
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**base,
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n_kv_heads=8,
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kv_lora_rank=32,
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q_lora_rank=64,
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qk_rope_head_dim=16,
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qk_nope_head_dim=16,
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v_head_dim=16,
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)
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model = OpenMythos(cfg)
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total = sum(p.numel() for p in model.parameters())
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print(f"\n[{attn_type.upper()}] Parameters: {total:,}")
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ids = torch.randint(0, cfg.vocab_size, (2, 16))
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logits = model(ids, n_loops=4)
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print(f"[{attn_type.upper()}] Logits shape: {logits.shape}")
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out = model.generate(ids, max_new_tokens=8, n_loops=8)
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print(f"[{attn_type.upper()}] Generated shape: {out.shape}")
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A = model.recurrent.injection.get_A()
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print(
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f"[{attn_type.upper()}] Spectral radius ρ(A) max: {A.max().item():.4f} (must be < 1)"
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)
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```
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## Documentation
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| Page | Description |
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|---|---|
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| [`docs/open_mythos.md`](docs/open_mythos.md) | Full API reference for the `OpenMythos` class — constructor, `forward`, `generate`, all sub-modules, configuration reference, and usage examples |
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---
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## The Central Hypothesis
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The injection of `e` at every step is what prevents the model from drifting — it keeps the original input signal alive throughout the entire recurrence depth.
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The full implementation is in [`open_mythos/main.py`](open_mythos/main.py). See the [`OpenMythos` class reference](docs/open_mythos.md) for a detailed API walkthrough, configuration options, and usage examples.
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---
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## Why This Explains Mythos
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- Reasoning with Latent Thoughts — On the Power of Looped Transformers: https://arxiv.org/abs/2502.17416
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- Training Large Language Models to Reason in a Continuous Latent Space: https://arxiv.org/abs/2412.06769
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- Relaxed Recursive Transformers — Effective Parameter Sharing with Layer-wise LoRA: https://arxiv.org/pdf/2410.20672
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---
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## Citation
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If you use OpenMythos in your research or build on this work, please cite:
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```bibtex
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@software{gomez2026openmythos,
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author = {Kye Gomez},
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title = {OpenMythos: A Theoretical Reconstruction of the Claude Mythos Architecture},
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year = {2026},
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url = {https://github.com/kyegomez/OpenMythos},
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note = {Recurrent-Depth Transformer with MoE, MLA, LTI-stable injection, and ACT halting}
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}
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```
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---
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## License
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MIT License — Copyright (c) 2026 Kye Gomez. See [`LICENSE`](LICENSE) for the full text.
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docs/open_mythos.md
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# `OpenMythos` — Class Reference
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| 2 |
+
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| 3 |
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**Module:** `open_mythos.main`
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| 4 |
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**Base class:** `torch.nn.Module`
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| 5 |
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---
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| 7 |
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## Overview
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| 9 |
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`OpenMythos` is the top-level model class implementing the Recurrent-Depth Transformer (RDT) architecture described in [the OpenMythos hypothesis](../README.md). It assembles three functional stages — **Prelude**, **Recurrent Block**, and **Coda** — into a complete autoregressive language model.
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```
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Input token IDs (B, T)
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| 14 |
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↓
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| 15 |
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[Embedding] token index → dim-dimensional vector
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| 16 |
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↓
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| 17 |
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[Prelude] prelude_layers × standard TransformerBlock (run once)
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| 18 |
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↓
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| 19 |
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[Recurrent Block] one TransformerBlock looped T times
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| 20 |
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↑___________↓ h_{t+1} = A·h_t + B·e + Transformer(h_t, e)
|
| 21 |
+
↓
|
| 22 |
+
[Coda] coda_layers × standard TransformerBlock (run once)
|
| 23 |
+
↓
|
| 24 |
+
[RMSNorm → LM head]
|
| 25 |
+
↓
|
| 26 |
+
Output logits (B, T, vocab_size)
|
| 27 |
+
```
|
| 28 |
+
|
| 29 |
+
Every architectural choice in `OpenMythos` can be configured through a single [`MythosConfig`](#mythosconfig) dataclass passed at construction.
|
| 30 |
+
|
| 31 |
+
---
|
| 32 |
+
|
| 33 |
+
## `MythosConfig`
|
| 34 |
+
|
| 35 |
+
```python
|
| 36 |
+
@dataclass
|
| 37 |
+
class MythosConfig
|
| 38 |
+
```
|
| 39 |
+
|
| 40 |
+
All hyperparameters for the model are stored in this single frozen-style dataclass. Pass an instance to `OpenMythos.__init__`.
|
| 41 |
+
|
| 42 |
+
### Core fields
|
| 43 |
+
|
| 44 |
+
| Field | Type | Default | Description |
|
| 45 |
+
|---|---|---|---|
|
| 46 |
+
| `vocab_size` | `int` | `32000` | Token vocabulary size; sets the embedding and LM head dimension |
|
| 47 |
+
| `dim` | `int` | `2048` | Model hidden dimension — the width of the residual stream throughout |
|
| 48 |
+
| `n_heads` | `int` | `16` | Number of query attention heads |
|
| 49 |
+
| `n_kv_heads` | `int` | `4` | Number of key/value heads (GQA only); `n_heads // n_kv_heads` Q heads share each KV pair |
|
| 50 |
+
| `max_seq_len` | `int` | `4096` | Maximum sequence length; RoPE frequencies are precomputed up to this length |
|
| 51 |
+
| `max_loop_iters` | `int` | `16` | Default recurrent loop depth T at inference. Can be overridden per call |
|
| 52 |
+
| `prelude_layers` | `int` | `2` | Number of standard transformer blocks run once before the recurrent loop |
|
| 53 |
+
| `coda_layers` | `int` | `2` | Number of standard transformer blocks run once after the recurrent loop |
|
| 54 |
+
|
| 55 |
+
### Attention fields
|
| 56 |
+
|
| 57 |
+
`attn_type` selects between two complete attention implementations. All other attention fields are implementation-specific.
|
| 58 |
+
|
| 59 |
+
| Field | Type | Default | Description |
|
| 60 |
+
|---|---|---|---|
|
| 61 |
+
| `attn_type` | `str` | `"mla"` | `"gqa"` for Grouped Query Attention; `"mla"` for Multi-Latent Attention |
|
| 62 |
+
| `kv_lora_rank` | `int` | `512` | **[MLA only]** Compressed KV latent rank stored in the cache instead of full K and V |
|
| 63 |
+
| `q_lora_rank` | `int` | `1536` | **[MLA only]** Compressed Q latent rank |
|
| 64 |
+
| `qk_rope_head_dim` | `int` | `64` | **[MLA only]** Per-head dimension receiving RoPE positional encoding |
|
| 65 |
+
| `qk_nope_head_dim` | `int` | `128` | **[MLA only]** Per-head dimension without positional encoding |
|
| 66 |
+
| `v_head_dim` | `int` | `128` | **[MLA only]** Per-head value dimension |
|
| 67 |
+
|
| 68 |
+
**GQA vs MLA:** GQA reduces KV cache by having fewer KV heads than Q heads (factor of `n_heads / n_kv_heads`). MLA achieves a much larger reduction by caching a low-rank KV latent (`kv_lora_rank`) and the RoPE keys (`n_heads × qk_rope_head_dim`), then reconstructing full K and V on the fly. At production scale MLA yields roughly 10–20× smaller KV cache than standard attention.
|
| 69 |
+
|
| 70 |
+
### MoE FFN fields
|
| 71 |
+
|
| 72 |
+
The Mixture-of-Experts FFN is used exclusively inside the Recurrent Block. Prelude and Coda use a dense SwiGLU FFN.
|
| 73 |
+
|
| 74 |
+
| Field | Type | Default | Description |
|
| 75 |
+
|---|---|---|---|
|
| 76 |
+
| `n_experts` | `int` | `64` | Total number of routed expert FFNs |
|
| 77 |
+
| `n_shared_experts` | `int` | `2` | Always-active shared experts; absorb common cross-domain patterns |
|
| 78 |
+
| `n_experts_per_tok` | `int` | `4` | Top-K routed experts selected per token by the router |
|
| 79 |
+
| `expert_dim` | `int` | `512` | Hidden dimension inside each fine-grained routed expert |
|
| 80 |
+
|
| 81 |
+
Approximately `n_experts_per_tok / n_experts = 6.25%` of routed expert parameters are activated per token, plus all shared expert parameters.
|
| 82 |
+
|
| 83 |
+
### Stability and adaptation fields
|
| 84 |
+
|
| 85 |
+
| Field | Type | Default | Description |
|
| 86 |
+
|---|---|---|---|
|
| 87 |
+
| `act_threshold` | `float` | `0.99` | ACT cumulative halting threshold; loop exits per-position once this is exceeded |
|
| 88 |
+
| `rope_theta` | `float` | `500000.0` | RoPE base frequency (LLaMA-3 default; higher = slower frequency decay over sequence positions) |
|
| 89 |
+
| `lora_rank` | `int` | `16` | Rank of the depth-wise LoRA adapter applied inside each loop iteration |
|
| 90 |
+
|
| 91 |
+
---
|
| 92 |
+
|
| 93 |
+
## Constructor
|
| 94 |
+
|
| 95 |
+
```python
|
| 96 |
+
OpenMythos(cfg: MythosConfig)
|
| 97 |
+
```
|
| 98 |
+
|
| 99 |
+
Builds all sub-modules, precomputes RoPE frequency buffers, and runs weight initialization.
|
| 100 |
+
|
| 101 |
+
**What happens internally:**
|
| 102 |
+
|
| 103 |
+
1. `nn.Embedding(vocab_size, dim)` — token embedding table, weight-tied with the LM head.
|
| 104 |
+
2. RoPE buffers — `freqs_cis` (for GQA, dim = `dim // n_heads`) and `freqs_cis_mla` (for MLA, dim = `qk_rope_head_dim`) are precomputed once and registered as non-parameter buffers. The correct buffer is selected at forward time based on `cfg.attn_type`.
|
| 105 |
+
3. `prelude` — `nn.ModuleList` of `prelude_layers` `TransformerBlock` instances with dense SwiGLU FFN.
|
| 106 |
+
4. `recurrent` — a single `RecurrentBlock` containing one `TransformerBlock` (with MoE FFN), `LTIInjection`, `ACTHalting`, and `LoRAAdapter`.
|
| 107 |
+
5. `coda` — `nn.ModuleList` of `coda_layers` `TransformerBlock` instances with dense SwiGLU FFN.
|
| 108 |
+
6. `RMSNorm(dim)` applied before the LM head.
|
| 109 |
+
7. `nn.Linear(dim, vocab_size, bias=False)` LM head with weights tied to the embedding.
|
| 110 |
+
8. All `nn.Linear` and `nn.Embedding` weights initialized from N(0, 0.02).
|
| 111 |
+
|
| 112 |
+
**Example:**
|
| 113 |
+
|
| 114 |
+
```python
|
| 115 |
+
from open_mythos.main import OpenMythos, MythosConfig
|
| 116 |
+
|
| 117 |
+
cfg = MythosConfig(
|
| 118 |
+
vocab_size=32000,
|
| 119 |
+
dim=2048,
|
| 120 |
+
n_heads=16,
|
| 121 |
+
n_kv_heads=4,
|
| 122 |
+
max_loop_iters=16,
|
| 123 |
+
attn_type="mla",
|
| 124 |
+
)
|
| 125 |
+
model = OpenMythos(cfg)
|
| 126 |
+
print(f"Parameters: {sum(p.numel() for p in model.parameters()):,}")
|
| 127 |
+
```
|
| 128 |
+
|
| 129 |
+
---
|
| 130 |
+
|
| 131 |
+
## `forward`
|
| 132 |
+
|
| 133 |
+
```python
|
| 134 |
+
def forward(
|
| 135 |
+
self,
|
| 136 |
+
input_ids: torch.Tensor,
|
| 137 |
+
n_loops: Optional[int] = None,
|
| 138 |
+
kv_cache: Optional[dict] = None,
|
| 139 |
+
) -> torch.Tensor
|
| 140 |
+
```
|
| 141 |
+
|
| 142 |
+
Single forward pass through the full Prelude → Recurrent Block → Coda pipeline.
|
| 143 |
+
|
| 144 |
+
### Parameters
|
| 145 |
+
|
| 146 |
+
| Parameter | Type | Description |
|
| 147 |
+
|---|---|---|
|
| 148 |
+
| `input_ids` | `Tensor (B, T)` | Batch of token index sequences. `B` = batch size, `T` = sequence length |
|
| 149 |
+
| `n_loops` | `int \| None` | Recurrent loop depth for this call. Defaults to `cfg.max_loop_iters`. Pass a higher value at inference to extrapolate to harder problems (depth extrapolation property). |
|
| 150 |
+
| `kv_cache` | `dict \| None` | If provided, keys and values are accumulated here for autoregressive decoding. Pass `{}` on the first decode step and reuse the same dict across steps. Pass `None` for training or full-context inference. |
|
| 151 |
+
|
| 152 |
+
### Returns
|
| 153 |
+
|
| 154 |
+
`Tensor (B, T, vocab_size)` — raw (unnormalized) logits over the vocabulary for each position.
|
| 155 |
+
|
| 156 |
+
### Behavior walkthrough
|
| 157 |
+
|
| 158 |
+
```
|
| 159 |
+
1. Embed: x = embedding(input_ids) # (B, T, dim)
|
| 160 |
+
2. Select RoPE buffer:
|
| 161 |
+
if attn_type == "mla": use freqs_cis_mla[:T]
|
| 162 |
+
else: use freqs_cis[:T]
|
| 163 |
+
3. Build causal mask (upper-triangular -inf):
|
| 164 |
+
if T > 1: mask = _causal_mask(T, device)
|
| 165 |
+
else: mask = None (single-token decode step)
|
| 166 |
+
4. Prelude:
|
| 167 |
+
for i, layer in prelude:
|
| 168 |
+
x = layer(x, freqs_cis, mask, kv_cache, f"prelude_{i}")
|
| 169 |
+
5. Freeze encoded input:
|
| 170 |
+
e = x # (B, T, dim)
|
| 171 |
+
6. Recurrent loop:
|
| 172 |
+
x = recurrent(x, e, freqs_cis, mask, n_loops, kv_cache)
|
| 173 |
+
7. Coda:
|
| 174 |
+
for i, layer in coda:
|
| 175 |
+
x = layer(x, freqs_cis, mask, kv_cache, f"coda_{i}")
|
| 176 |
+
8. Project: logits = lm_head(norm(x)) # (B, T, vocab_size)
|
| 177 |
+
```
|
| 178 |
+
|
| 179 |
+
**Step 5 (freeze `e`)** is the key architectural invariant: the encoded input `e` is captured after the Prelude and injected at *every* loop iteration unchanged. This prevents the hidden state from drifting away from the original input signal regardless of loop depth.
|
| 180 |
+
|
| 181 |
+
### Training example
|
| 182 |
+
|
| 183 |
+
```python
|
| 184 |
+
import torch
|
| 185 |
+
from open_mythos.main import OpenMythos, MythosConfig
|
| 186 |
+
|
| 187 |
+
model = OpenMythos(MythosConfig()).cuda()
|
| 188 |
+
optimizer = torch.optim.AdamW(model.parameters(), lr=3e-4)
|
| 189 |
+
|
| 190 |
+
input_ids = torch.randint(0, 32000, (2, 512)).cuda()
|
| 191 |
+
labels = torch.randint(0, 32000, (2, 512)).cuda()
|
| 192 |
+
|
| 193 |
+
logits = model(input_ids) # (2, 512, 32000)
|
| 194 |
+
loss = torch.nn.functional.cross_entropy(
|
| 195 |
+
logits.view(-1, 32000),
|
| 196 |
+
labels.view(-1),
|
| 197 |
+
)
|
| 198 |
+
loss.backward()
|
| 199 |
+
optimizer.step()
|
| 200 |
+
```
|
| 201 |
+
|
| 202 |
+
### Depth extrapolation at inference
|
| 203 |
+
|
| 204 |
+
A looped transformer trained on `N` loops can be evaluated on `N + k` loops and often achieves higher quality on hard multi-hop problems. Pass `n_loops` at inference time:
|
| 205 |
+
|
| 206 |
+
```python
|
| 207 |
+
# Trained with max_loop_iters=16 — try deeper reasoning at test time
|
| 208 |
+
logits_deep = model(input_ids, n_loops=32)
|
| 209 |
+
```
|
| 210 |
+
|
| 211 |
+
---
|
| 212 |
+
|
| 213 |
+
## `generate`
|
| 214 |
+
|
| 215 |
+
```python
|
| 216 |
+
@torch.no_grad()
|
| 217 |
+
def generate(
|
| 218 |
+
self,
|
| 219 |
+
input_ids: torch.Tensor,
|
| 220 |
+
max_new_tokens: int = 64,
|
| 221 |
+
n_loops: int = 8,
|
| 222 |
+
temperature: float = 1.0,
|
| 223 |
+
top_k: int = 50,
|
| 224 |
+
) -> torch.Tensor
|
| 225 |
+
```
|
| 226 |
+
|
| 227 |
+
Autoregressive token generation with KV caching. Processes the full prompt on step 0, then decodes one token at a time using the accumulated cache.
|
| 228 |
+
|
| 229 |
+
### Parameters
|
| 230 |
+
|
| 231 |
+
| Parameter | Type | Default | Description |
|
| 232 |
+
|---|---|---|---|
|
| 233 |
+
| `input_ids` | `Tensor (B, T)` | — | Prompt token indices |
|
| 234 |
+
| `max_new_tokens` | `int` | `64` | Number of new tokens to generate |
|
| 235 |
+
| `n_loops` | `int` | `8` | Recurrent loop depth per decode step. Can be higher than the training value for harder prompts (depth extrapolation) |
|
| 236 |
+
| `temperature` | `float` | `1.0` | Softmax temperature applied to logits before sampling. Values < 1 make the distribution more peaked (less random); values > 1 make it flatter |
|
| 237 |
+
| `top_k` | `int` | `50` | Restricts sampling to the top-K most probable tokens at each step. `0` disables filtering (full vocabulary sampling) |
|
| 238 |
+
|
| 239 |
+
### Returns
|
| 240 |
+
|
| 241 |
+
`Tensor (B, T + max_new_tokens)` — the original prompt concatenated with the generated token indices.
|
| 242 |
+
|
| 243 |
+
### KV caching mechanism
|
| 244 |
+
|
| 245 |
+
On step 0, the full prompt `(B, T)` is passed and all keys/values for every layer are populated in `kv_cache`. On steps 1…N only the single most recent token `(B, 1)` is passed; the attention layers read back all prior K/V from the cache. This makes decode cost proportional to a single token per step rather than the full growing sequence.
|
| 246 |
+
|
| 247 |
+
Each layer caches under a deterministic string key (`"prelude_0"`, `"recurrent_loop_3"`, `"coda_1"`, etc.), so caches from different layers never collide.
|
| 248 |
+
|
| 249 |
+
### Sampling strategy
|
| 250 |
+
|
| 251 |
+
```
|
| 252 |
+
logits = forward(cur_ids, n_loops, kv_cache)[:, -1, :] / temperature
|
| 253 |
+
|
| 254 |
+
if top_k > 0:
|
| 255 |
+
threshold = logits.topk(top_k).values[:, -1:]
|
| 256 |
+
logits[logits < threshold] = -inf
|
| 257 |
+
|
| 258 |
+
probs = softmax(logits)
|
| 259 |
+
next_tok = multinomial(probs, num_samples=1)
|
| 260 |
+
```
|
| 261 |
+
|
| 262 |
+
### Generation example
|
| 263 |
+
|
| 264 |
+
```python
|
| 265 |
+
import torch
|
| 266 |
+
from open_mythos.main import OpenMythos, MythosConfig
|
| 267 |
+
|
| 268 |
+
model = OpenMythos(MythosConfig()).eval()
|
| 269 |
+
|
| 270 |
+
# Tokenized prompt (use your tokenizer of choice)
|
| 271 |
+
prompt = torch.tensor([[1, 450, 3118, 310, 278]]) # (1, 5)
|
| 272 |
+
|
| 273 |
+
output = model.generate(
|
| 274 |
+
prompt,
|
| 275 |
+
max_new_tokens=128,
|
| 276 |
+
n_loops=16, # deeper reasoning
|
| 277 |
+
temperature=0.8,
|
| 278 |
+
top_k=40,
|
| 279 |
+
)
|
| 280 |
+
# output.shape == (1, 133)
|
| 281 |
+
```
|
| 282 |
+
|
| 283 |
+
---
|
| 284 |
+
|
| 285 |
+
## Internal Components
|
| 286 |
+
|
| 287 |
+
The following sub-modules are assembled inside `OpenMythos`. They are not typically called directly but understanding them clarifies the model's behavior.
|
| 288 |
+
|
| 289 |
+
### `RecurrentBlock`
|
| 290 |
+
|
| 291 |
+
The heart of the architecture. A single `TransformerBlock` (with MoE FFN) is run in a loop for up to `n_loops` iterations, with the following per-iteration pipeline:
|
| 292 |
+
|
| 293 |
+
```
|
| 294 |
+
h_loop = loop_index_embedding(h, t, loop_dim) # inject sinusoidal loop-index signal
|
| 295 |
+
combined = RMSNorm(h_loop + e) # add frozen encoded input
|
| 296 |
+
trans_out = TransformerBlock(combined, ...) # attention + MoE FFN
|
| 297 |
+
trans_out = trans_out + LoRAAdapter(trans_out, t) # depth-wise LoRA delta
|
| 298 |
+
h = LTIInjection(h, e, trans_out) # stable update: A·h + B·e + trans_out
|
| 299 |
+
p = ACTHalting(h) # per-position halting probability
|
| 300 |
+
```
|
| 301 |
+
|
| 302 |
+
The loop exits early for positions whose cumulative halting probability exceeds `cfg.act_threshold`. If all positions have halted, the loop exits before `n_loops`. The final output is an ACT-weighted sum of `h` across iterations.
|
| 303 |
+
|
| 304 |
+
### `LTIInjection`
|
| 305 |
+
|
| 306 |
+
Implements the stable recurrent update rule `h_{t+1} = A·h_t + B·e + transformer_out`. The diagonal matrix `A` is parameterized as:
|
| 307 |
+
|
| 308 |
+
```
|
| 309 |
+
A_continuous = Diag(-exp(log_A)) # always negative diagonal
|
| 310 |
+
A_discrete = exp(Δt · A_continuous) # ZOH discretization, values ∈ (0, 1)
|
| 311 |
+
```
|
| 312 |
+
|
| 313 |
+
This guarantees spectral radius `ρ(A) < 1` by construction, making the looped model unconditionally stable regardless of learning rate or batch noise. See [Parcae (Prairie et al., 2026)](https://arxiv.org/abs/2604.12946) for the theoretical foundation.
|
| 314 |
+
|
| 315 |
+
### `ACTHalting`
|
| 316 |
+
|
| 317 |
+
A single linear layer mapping `(B, T, dim) → (B, T)` followed by sigmoid. At each loop step, the scalar halting probability per position is accumulated. When the cumulative sum exceeds `cfg.act_threshold`, the ACT remainder trick assigns the remaining probability mass as the final weight and the position stops contributing. Implements Graves (2016) ACT.
|
| 318 |
+
|
| 319 |
+
### `LoRAAdapter`
|
| 320 |
+
|
| 321 |
+
A depth-wise low-rank adapter with three components:
|
| 322 |
+
|
| 323 |
+
- `down`: shared `Linear(dim, rank)` — down-projects the transformer output
|
| 324 |
+
- `B`: shared parameter matrix `(rank, dim)` — up-projects back to full dimension
|
| 325 |
+
- `scale`: `Embedding(max_loops, rank)` — per-loop element-wise scale
|
| 326 |
+
|
| 327 |
+
The delta per iteration is `(down(x) * scale[t]) @ B`. Bridges the expressiveness gap between pure weight-tying and fully distinct per-layer weights. Based on [Relaxed Recursive Transformers (Bae et al., 2024)](https://arxiv.org/pdf/2410.20672).
|
| 328 |
+
|
| 329 |
+
### `TransformerBlock`
|
| 330 |
+
|
| 331 |
+
Pre-norm transformer block with swappable attention and FFN:
|
| 332 |
+
|
| 333 |
+
- **Attention:** `MLAttention` (MLA) or `GQAttention` (GQA), selected by `cfg.attn_type`
|
| 334 |
+
- **FFN:** `MoEFFN` (when `use_moe=True`, inside `RecurrentBlock`) or dense `Expert` (Prelude, Coda)
|
| 335 |
+
- Pre-norm via `RMSNorm` applied to both the attention input and FFN input
|
| 336 |
+
|
| 337 |
+
### `MLAttention`
|
| 338 |
+
|
| 339 |
+
Multi-Latent Attention ([DeepSeek-V2, 2024](https://arxiv.org/abs/2405.04434)). The cache stores only the compressed KV latent `c_kv` (rank `kv_lora_rank`) plus the RoPE-encoded keys. At each decode step, `K_nope` and `V` are cheaply reconstructed from `c_kv` via a shared up-projection, trading a fast linear multiply for dramatically smaller KV memory footprint.
|
| 340 |
+
|
| 341 |
+
Cache size per layer per token: `kv_lora_rank + n_heads × qk_rope_head_dim` vs. full GQA cache of `n_kv_heads × head_dim × 2`.
|
| 342 |
+
|
| 343 |
+
### `GQAttention`
|
| 344 |
+
|
| 345 |
+
Grouped Query Attention ([Ainslie et al., 2023](https://arxiv.org/abs/2305.13245)). `n_kv_heads` KV pairs are shared across `n_heads // n_kv_heads` query heads each, reducing KV cache by that factor while preserving full query expressiveness.
|
| 346 |
+
|
| 347 |
+
### `MoEFFN`
|
| 348 |
+
|
| 349 |
+
Fine-grained Mixture-of-Experts FFN ([DeepSeekMoE, Dai et al., 2024](https://arxiv.org/abs/2401.06066)):
|
| 350 |
+
|
| 351 |
+
- **Routed experts:** `n_experts` small SwiGLU FFNs. Each token's router selects the top-`n_experts_per_tok` via softmax over learned logits. A per-expert bias `router_bias` (non-gradient, updated externally) keeps load balanced.
|
| 352 |
+
- **Shared experts:** `n_shared_experts` always-active FFNs with width `expert_dim × n_experts_per_tok`, absorbing cross-domain patterns.
|
| 353 |
+
|
| 354 |
+
Total activated parameters per token: `(n_experts_per_tok / n_experts)` of routed capacity + all shared capacity.
|
| 355 |
+
|
| 356 |
+
### `Expert`
|
| 357 |
+
|
| 358 |
+
Single SwiGLU feed-forward unit: `down(silu(gate(x)) * up(x))`. Used both as individual routed experts inside `MoEFFN` and as the dense FFN in Prelude/Coda blocks.
|
| 359 |
+
|
| 360 |
+
### `RMSNorm`
|
| 361 |
+
|
| 362 |
+
Root Mean Square Layer Normalization ([Zhang & Sennrich, 2019](https://arxiv.org/abs/1910.07467)). Normalizes by `x / rms(x)` with a learned per-channel rescaling weight. No bias, no mean subtraction. Used throughout in place of standard LayerNorm.
|
| 363 |
+
|
| 364 |
+
---
|
| 365 |
+
|
| 366 |
+
## Utility functions
|
| 367 |
+
|
| 368 |
+
### `precompute_rope_freqs(dim, max_len, theta)`
|
| 369 |
+
|
| 370 |
+
Precomputes complex-valued RoPE rotation matrices as a `(max_len, dim//2)` complex64 tensor. Called once in `__init__` and stored as a buffer.
|
| 371 |
+
|
| 372 |
+
### `apply_rope(x, freqs_cis)`
|
| 373 |
+
|
| 374 |
+
Applies precomputed RoPE frequencies to a query or key tensor by treating adjacent feature pairs as complex numbers and multiplying pointwise by the positional phasor.
|
| 375 |
+
|
| 376 |
+
### `loop_index_embedding(h, loop_t, loop_dim, theta)`
|
| 377 |
+
|
| 378 |
+
Injects a sinusoidal loop-index signal into the first `loop_dim` channels of the hidden state, analogous to RoPE but over recurrence depth rather than sequence position. Allows the shared recurrent block weights to behave differently at different loop iterations.
|
| 379 |
+
|
| 380 |
+
---
|
| 381 |
+
|
| 382 |
+
## Key design properties
|
| 383 |
+
|
| 384 |
+
| Property | Mechanism | Benefit |
|
| 385 |
+
|---|---|---|
|
| 386 |
+
| Depth extrapolation | Recurrent block with looped identical weights | Train on N loops, test on N+k — harder problems solved without retraining |
|
| 387 |
+
| Parameter efficiency | Weight sharing across all loop iterations | k-layer model achieves quality of kL-layer model; parameters ≈ k, compute ∝ L |
|
| 388 |
+
| Adaptive compute | ACT halting per position | Easy tokens exit early; hard tokens receive full loop depth — within the same batch |
|
| 389 |
+
| Stable training | LTI injection with ZOH-constrained A (ρ(A) < 1) | No residual explosion; robust to high learning rates |
|
| 390 |
+
| Domain breadth | MoE FFN in recurrent block | Different expert subsets can be routed to at each loop depth |
|
| 391 |
+
| Loop differentiation | Loop-index sinusoidal embedding | Same weights implement functionally distinct phases per iteration |
|
| 392 |
+
| Efficient KV memory | MLA (default) or GQA | MLA: 10–20× smaller cache vs standard attention at production scale |
|
| 393 |
+
| Depth-wise adaptation | LoRA adapter per loop iteration | Expressiveness beyond pure weight-tying; minimal parameter overhead |
|
| 394 |
+
|
| 395 |
+
---
|
| 396 |
+
|
| 397 |
+
## Full configuration reference
|
| 398 |
+
|
| 399 |
+
The default `MythosConfig()` targets a mid-scale research model. Below is a minimal configuration for quick experimentation:
|
| 400 |
+
|
| 401 |
+
```python
|
| 402 |
+
from open_mythos.main import OpenMythos, MythosConfig
|
| 403 |
+
|
| 404 |
+
# Minimal config for fast iteration / unit testing
|
| 405 |
+
small_cfg = MythosConfig(
|
| 406 |
+
vocab_size=8192,
|
| 407 |
+
dim=256,
|
| 408 |
+
n_heads=4,
|
| 409 |
+
n_kv_heads=2,
|
| 410 |
+
max_seq_len=512,
|
| 411 |
+
max_loop_iters=4,
|
| 412 |
+
prelude_layers=1,
|
| 413 |
+
coda_layers=1,
|
| 414 |
+
attn_type="gqa",
|
| 415 |
+
n_experts=8,
|
| 416 |
+
n_shared_experts=1,
|
| 417 |
+
n_experts_per_tok=2,
|
| 418 |
+
expert_dim=64,
|
| 419 |
+
lora_rank=4,
|
| 420 |
+
)
|
| 421 |
+
model = OpenMythos(small_cfg)
|
| 422 |
+
```
|
| 423 |
+
|
| 424 |
+
And a production-oriented MLA configuration matching the default hyperparameters:
|
| 425 |
+
|
| 426 |
+
```python
|
| 427 |
+
# Default MLA config (matches MythosConfig() defaults)
|
| 428 |
+
prod_cfg = MythosConfig(
|
| 429 |
+
vocab_size=32000,
|
| 430 |
+
dim=2048,
|
| 431 |
+
n_heads=16,
|
| 432 |
+
n_kv_heads=4,
|
| 433 |
+
max_seq_len=4096,
|
| 434 |
+
max_loop_iters=16,
|
| 435 |
+
prelude_layers=2,
|
| 436 |
+
coda_layers=2,
|
| 437 |
+
attn_type="mla", # Multi-Latent Attention
|
| 438 |
+
kv_lora_rank=512,
|
| 439 |
+
q_lora_rank=1536,
|
| 440 |
+
qk_rope_head_dim=64,
|
| 441 |
+
qk_nope_head_dim=128,
|
| 442 |
+
v_head_dim=128,
|
| 443 |
+
n_experts=64,
|
| 444 |
+
n_shared_experts=2,
|
| 445 |
+
n_experts_per_tok=4,
|
| 446 |
+
expert_dim=512,
|
| 447 |
+
act_threshold=0.99,
|
| 448 |
+
rope_theta=500000.0,
|
| 449 |
+
lora_rank=16,
|
| 450 |
+
)
|
| 451 |
+
model = OpenMythos(prod_cfg)
|
| 452 |
+
```
|
| 453 |
+
|
| 454 |
+
---
|
| 455 |
+
|
| 456 |
+
## References
|
| 457 |
+
|
| 458 |
+
| Component | Paper |
|
| 459 |
+
|---|---|
|
| 460 |
+
| Recurrent-Depth Transformer | [Loop, Think, & Generalize (2025)](https://arxiv.org/pdf/2604.07822) |
|
| 461 |
+
| LTI-stable injection (Parcae) | [Scaling Laws for Stable Looped Language Models (Prairie et al., 2026)](https://arxiv.org/abs/2604.12946) |
|
| 462 |
+
| Looped transformer reasoning | [Reasoning with Latent Thoughts (Saunshi et al., 2025)](https://arxiv.org/abs/2502.17416) |
|
| 463 |
+
| Multi-Latent Attention | [DeepSeek-V2 (2024)](https://arxiv.org/abs/2405.04434) |
|
| 464 |
+
| Grouped Query Attention | [Ainslie et al., 2023](https://arxiv.org/abs/2305.13245) |
|
| 465 |
+
| Mixture-of-Experts FFN | [DeepSeekMoE (Dai et al., 2024)](https://arxiv.org/abs/2401.06066) |
|
| 466 |
+
| Adaptive Computation Time | [Graves, 2016](https://arxiv.org/abs/1603.08983) |
|
| 467 |
+
| Depth-wise LoRA | [Relaxed Recursive Transformers (Bae et al., 2024)](https://arxiv.org/pdf/2410.20672) |
|
| 468 |
+
| RMSNorm | [Zhang & Sennrich, 2019](https://arxiv.org/abs/1910.07467) |
|
| 469 |
+
| RoPE | [Su et al., 2021](https://arxiv.org/abs/2104.09864) |
|
| 470 |
+
| Universal Transformer (ACT basis) | [Dehghani et al., 2018](https://arxiv.org/pdf/1807.03819) |
|
| 471 |
+
| Continuous latent reasoning | [COCONUT (2024)](https://arxiv.org/abs/2412.06769) |
|