feat: add OpenThoughts-TBLite evaluation environment and configuration files

Introduced a new evaluation environment for OpenThoughts-TBLite, including the main evaluation script, configuration YAML, and README documentation. This environment provides a faster alternative to Terminal-Bench 2.0, featuring 100 difficulty-calibrated tasks for terminal agents. The setup allows for easy evaluation and configuration, enhancing the benchmarking capabilities for terminal agents.

environments/benchmarks/tblite/README.md

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+# OpenThoughts-TBLite Evaluation Environment
+
+This environment evaluates terminal agents on the [OpenThoughts-TBLite](https://huggingface.co/datasets/open-thoughts/OpenThoughts-TBLite) benchmark, a difficulty-calibrated subset of [Terminal-Bench 2.0](https://www.tbench.ai/leaderboard/terminal-bench/2.0).
+
+## Source
+
+OpenThoughts-TBLite was created by the [OpenThoughts](https://www.openthoughts.ai/) Agent team in collaboration with [Snorkel AI](https://snorkel.ai/) and [Bespoke Labs](https://bespokelabs.ai/). The original dataset and documentation live at:
+
+- **Dataset (source):** [open-thoughts/OpenThoughts-TBLite](https://huggingface.co/datasets/open-thoughts/OpenThoughts-TBLite)
+- **GitHub:** [open-thoughts/OpenThoughts-TBLite](https://github.com/open-thoughts/OpenThoughts-TBLite)
+- **Blog post:** [openthoughts.ai/blog/openthoughts-tblite](https://www.openthoughts.ai/blog/openthoughts-tblite)
+
+## Our Dataset
+
+We converted the source into the same schema used by our Terminal-Bench 2.0 environment (pre-built Docker Hub images, base64-encoded test tarballs, etc.) and published it as:
+
+- **Dataset (ours):** [NousResearch/openthoughts-tblite](https://huggingface.co/datasets/NousResearch/openthoughts-tblite)
+- **Docker images:** `nousresearch/tblite-<task-name>:latest` on Docker Hub (100 images)
+
+The conversion script is at `scripts/prepare_tblite_dataset.py`.
+
+## Why TBLite?
+
+Terminal-Bench 2.0 is one of the strongest frontier evaluations for terminal agents, but when a model scores near the floor (e.g., Qwen 3 8B at <1%), many changes look identical in aggregate score. TBLite addresses this by calibrating task difficulty using Claude Haiku 4.5 as a reference:
+
+| Difficulty | Pass Rate Range | Tasks |
+|------------|----------------|-------|
+| Easy       | >= 70%         | 40    |
+| Medium     | 40-69%         | 26    |
+| Hard       | 10-39%         | 26    |
+| Extreme    | < 10%          | 8     |
+
+This gives enough solvable tasks to detect small improvements quickly, while preserving enough hard tasks to avoid saturation. The correlation between TBLite and TB2 scores is **r = 0.911**.
+
+TBLite also runs 2.6-8x faster than the full TB2, making it practical for iteration loops.
+
+## Usage
+
+```bash
+# Run the full benchmark
+python environments/benchmarks/tblite/tblite_env.py evaluate
+
+# Filter to specific tasks
+python environments/benchmarks/tblite/tblite_env.py evaluate \
+    --env.task_filter "broken-python,pandas-etl"
+
+# Use a different model
+python environments/benchmarks/tblite/tblite_env.py evaluate \
+    --server.model_name "qwen/qwen3-30b"
+```
+
+## Architecture
+
+`TBLiteEvalEnv` is a thin subclass of `TerminalBench2EvalEnv`. All evaluation logic (agent loop, Docker sandbox management, test verification, metrics) is inherited. Only the defaults differ:
+
+| Setting        | TB2                              | TBLite                                  |
+|----------------|----------------------------------|-----------------------------------------|
+| Dataset        | `NousResearch/terminal-bench-2`  | `NousResearch/openthoughts-tblite`      |
+| Tasks          | 89                               | 100                                     |
+| Task timeout   | 1800s (30 min)                   | 1200s (20 min)                          |
+| Wandb name     | `terminal-bench-2`               | `openthoughts-tblite`                   |
+
+## Citation
+
+```bibtex
+@software{OpenThoughts-TBLite,
+  author = {OpenThoughts-Agent team, Snorkel AI, Bespoke Labs},
+  month = Feb,
+  title = {{OpenThoughts-TBLite: A High-Signal Benchmark for Iterating on Terminal Agents}},
+  howpublished = {https://www.openthoughts.ai/blog/openthoughts-tblite},
+  year = {2026}
+}
+```

environments/benchmarks/tblite/default.yaml

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+# OpenThoughts-TBLite Evaluation -- Default Configuration
+#
+# Eval-only environment for the TBLite benchmark (100 difficulty-calibrated
+# terminal tasks, a faster proxy for Terminal-Bench 2.0).
+# Uses Modal terminal backend for per-task cloud-isolated sandboxes
+# and OpenRouter for inference.
+#
+# Usage:
+#   python environments/benchmarks/tblite/tblite_env.py evaluate \
+#       --config environments/benchmarks/tblite/default.yaml
+#
+#   # Override model:
+#   python environments/benchmarks/tblite/tblite_env.py evaluate \
+#       --config environments/benchmarks/tblite/default.yaml \
+#       --openai.model_name anthropic/claude-sonnet-4
+
+env:
+  enabled_toolsets: ["terminal", "file"]
+  max_agent_turns: 60
+  max_token_length: 32000
+  agent_temperature: 0.8
+  terminal_backend: "modal"
+  terminal_timeout: 300        # 5 min per command (builds, pip install)
+  tool_pool_size: 128          # thread pool for 100 parallel tasks
+  dataset_name: "NousResearch/openthoughts-tblite"
+  test_timeout: 600
+  task_timeout: 1200           # 20 min wall-clock per task (TBLite tasks are faster)
+  tokenizer_name: "NousResearch/Hermes-3-Llama-3.1-8B"
+  use_wandb: true
+  wandb_name: "openthoughts-tblite"
+  ensure_scores_are_not_same: false
+  data_dir_to_save_evals: "environments/benchmarks/evals/openthoughts-tblite"
+
+openai:
+  base_url: "https://openrouter.ai/api/v1"
+  model_name: "anthropic/claude-opus-4.6"
+  server_type: "openai"
+  health_check: false
+  # api_key loaded from OPENROUTER_API_KEY in .env

environments/benchmarks/tblite/tblite_env.py

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+"""
+OpenThoughts-TBLite Evaluation Environment
+
+A lighter, faster alternative to Terminal-Bench 2.0 for iterating on terminal
+agents. Uses the same evaluation logic as TerminalBench2EvalEnv but defaults
+to the NousResearch/openthoughts-tblite dataset (100 difficulty-calibrated
+tasks vs TB2's 89 harder tasks).
+
+TBLite tasks are a curated subset of TB2 with a difficulty distribution
+designed to give meaningful signal even for smaller models:
+  - Easy (40 tasks):   >= 70% pass rate with Claude Haiku 4.5
+  - Medium (26 tasks): 40-69% pass rate
+  - Hard (26 tasks):   10-39% pass rate
+  - Extreme (8 tasks): < 10% pass rate
+
+Usage:
+    python environments/benchmarks/tblite/tblite_env.py evaluate
+
+    # Filter to specific tasks:
+    python environments/benchmarks/tblite/tblite_env.py evaluate \\
+        --env.task_filter "broken-python,pandas-etl"
+"""
+
+import os
+import sys
+from pathlib import Path
+from typing import List, Tuple
+
+_repo_root = Path(__file__).resolve().parent.parent.parent.parent
+if str(_repo_root) not in sys.path:
+    sys.path.insert(0, str(_repo_root))
+
+from pydantic import Field
+
+from atroposlib.envs.base import EvalHandlingEnum
+from atroposlib.envs.server_handling.server_manager import APIServerConfig
+
+from environments.benchmarks.terminalbench_2.terminalbench2_env import (
+    TerminalBench2EvalConfig,
+    TerminalBench2EvalEnv,
+)
+
+
+class TBLiteEvalConfig(TerminalBench2EvalConfig):
+    """Configuration for the OpenThoughts-TBLite evaluation environment.
+
+    Inherits all TB2 config fields. Only the dataset default and task timeout
+    differ -- TBLite tasks are calibrated to be faster.
+    """
+
+    dataset_name: str = Field(
+        default="NousResearch/openthoughts-tblite",
+        description="HuggingFace dataset containing TBLite tasks.",
+    )
+
+    task_timeout: int = Field(
+        default=1200,
+        description="Maximum wall-clock seconds per task. TBLite tasks are "
+        "generally faster than TB2, so 20 minutes is usually sufficient.",
+    )
+
+
+class TBLiteEvalEnv(TerminalBench2EvalEnv):
+    """OpenThoughts-TBLite evaluation environment.
+
+    Inherits all evaluation logic from TerminalBench2EvalEnv (agent loop,
+    test verification, Docker image resolution, metrics, wandb logging).
+    Only the default configuration differs.
+    """
+
+    name = "openthoughts-tblite"
+    env_config_cls = TBLiteEvalConfig
+
+    @classmethod
+    def config_init(cls) -> Tuple[TBLiteEvalConfig, List[APIServerConfig]]:
+        env_config = TBLiteEvalConfig(
+            enabled_toolsets=["terminal", "file"],
+            disabled_toolsets=None,
+            distribution=None,
+
+            max_agent_turns=60,
+            max_token_length=16000,
+            agent_temperature=0.6,
+            system_prompt=None,
+
+            terminal_backend="modal",
+            terminal_timeout=300,
+
+            test_timeout=180,
+
+            # 100 tasks in parallel
+            tool_pool_size=128,
+
+            eval_handling=EvalHandlingEnum.STOP_TRAIN,
+            group_size=1,
+            steps_per_eval=1,
+            total_steps=1,
+
+            tokenizer_name="NousResearch/Hermes-3-Llama-3.1-8B",
+            use_wandb=True,
+            wandb_name="openthoughts-tblite",
+            ensure_scores_are_not_same=False,
+        )
+
+        server_configs = [
+            APIServerConfig(
+                base_url="https://openrouter.ai/api/v1",
+                model_name="anthropic/claude-sonnet-4",
+                server_type="openai",
+                api_key=os.getenv("OPENROUTER_API_KEY", ""),
+                health_check=False,
+            )
+        ]
+
+        return env_config, server_configs
+
+
+if __name__ == "__main__":
+    TBLiteEvalEnv.cli()