[pufit]

Anthropic released Claude Fable 5.2 today — claude-fable-5-2: $8 / $40 per MTok, cache write $10 (5m) / $16 (1h), cache read $0.20, 1M context, 128K output, default effort high, all five effort levels (https://platform.claude.com/docs/en/models/fable-5-2/overview, https://platform.claude.com/docs/en/about-claude/pricing). The composer picker already picks it up through Models-API discovery (6 h cache); what Nerve gets wrong without this change is everything keyed on the model id.

Pricing. MODEL_PRICING matched claude-fable-5-2 by the fable-5 substring, i.e. Fable 5.1's $10/$50 — and that row also charges cache reads at $1.00, which is the original Fable 5 rate; Fable 5.1 reads at $0.25 (0.025x, per the pricing page footnote). New rows fable-5-2 ($8/$40, read $0.20, write $10/$16) and fable-5-1 ($10/$50, read $0.25, write $12.50/$20) sit ahead of the bare fable-5 key, with precedence tests.

Built-in picker fallback. DEFAULT_FALLBACK_MODEL → claude-fable-5-2 (the list used when discovery is off or unavailable).

fable alias. _build_env now defaults ANTHROPIC_DEFAULT_FABLE_MODEL to DEFAULT_FALLBACK_MODEL, the way opus and haiku already track DEFAULT_MODEL / DEFAULT_FAST_MODEL: an Agent/Workflow call or a skill asking for fable gets Nerve's current Fable whatever the CLI's own default is. agent.model_aliases: {fable: …} overrides it, "" unsets it, Bedrock gets no default — the same rules as the other two. (A deliberate choice; drop that hunk if you'd rather leave fable to the CLI.)

claude-agent-sdk 0.2.176 → 0.2.180 (bundled Claude Code CLI 2.1.316 → 2.1.321, whose changelog entry adds Fable 5.2 as the default fable model). Measured with a one-word -p run on claude-fable-5-2 from both bundles: 2.1.316 answers but logs [claude-code:unrecognized_model], reports contextWindow: 200000 and prices the turn at Opus 5.5 rates ($4/$20 + $5 cache write → $0.019633 for 2 in / 4 out / 3,909 cache-write tokens); 2.1.321 reports contextWindow: 1000000 and the Fable 5.2 rates ($0.052036 for 2 / 4 / 5,186). sdk_delta is Nerve's primary cost source and the CLI's window drives its auto-compaction, so Fable 5.2 on the old CLI is booked at half price and compacted at a fifth of its context. The pyproject floor moves to 0.2.180 for the reason the earlier floors moved: the bundled CLI is what every session runs. The lock diff is the one package; 0.2.177–0.2.180 change no Python API (release notes: an optional on_failure hook option, CLI bumps). uv.lock was written with uv 0.12.0 — the version CI pins — which records revision = 3; the revision = 5 on main came from dependabot's newer uv. uv lock --check passes under 0.12.0.

The effort ladder (_MODEL_EFFORT_LEVELS) already covers 5.2 through the fable-5 key — all five levels, confirmed in the migration guide — so only test cases were added there. config.example.yaml, docs/config.md and the GET /api/setup/models example in docs/api.md follow.

Tests run (changed files + every test module importing claude_agent_sdk, on the bumped SDK): test_default_models test_setup_api test_usage_cache_ttl test_engine test_cache_policy test_config_resolution test_models_route test_claude_transport test_agent_extras test_autonomous_turns test_interactive test_tools_schemas test_system_prompt_transport test_static_system_prompt test_inference_principal test_session_context test_schedule_attribution test_external_mode_mcp test_observability_langfuse test_ask_form — 1061 passed. No web changes.

Rollout: a gateway restart after this merge needs uv sync first (new pin).

Generated by Nerve

[nerveai]

Nerve PR review · ✅ Ready to merge (once the backend CI job is green)

This PR teaches Nerve about Claude Fable 5.2 everywhere it looks up a model id. The SDK bump matters most. On CLI 2.1.316, a Fable 5.2 turn is charged at Opus 5.5 rates through sdk_delta, the Claude backend's primary cost source, and is compacted at a 200K window. The new fable-5-2 and fable-5-1 rows match Anthropic's published prices. That includes the 0.025x cache-read rate on 5.1, which the old shared fable-5 row charged at 4x. The specific rows are checked before the bare fable-5 key, and model ids carry no date suffix, so no snapshot id lands on the wrong row. The new fable alias default works like the opus and haiku ones: config overrides it, "" unsets it, and Bedrock is skipped. It changes nothing today, because CLI 2.1.321 already defaults fable to 5.2.

Completeness: the precedence and alias tests would fail without the fix. config.example.yaml, docs/config.md and docs/api.md are updated. The lock diff touches only this package, and there is no migration.

_{Checked: 8 touched and related test modules in an offline sandbox at f8afbca: 561 passed, run on main's SDK 0.2.176, so the new SDK is exercised only by CI "Backend tests", which was still running. Also checked: the SDK v0.2.176→v0.2.180 source diff (only HookMatcher.on_failure changed; Nerve's SubprocessCLITransport and message_parser seams are untouched), the artifact hashes, and the rates against platform.claude.com pricing · automated review by nerveai — mention @nerveai to ask a follow-up.}