fix(claude): stop downgrading adaptive thinking on claude-haiku-5-5 (#15841)

⚠️ base-red inherited: #15306

Validated in local merge-train _artifacts/merge-wave-13/train2.log on devbox-vm-06-dev002 @ 59b137edc8bd23f9c95db60d65fa6dbc5ef00743 (FAST). All 13 boarded. Static gates green except inherited translation drift of docs/reference/ENVIRONMENT.md, the same violations on origin/release/v3.8.52. Changed node:test files passed 90/90 on rerun. The RTL sidebar test passed 19/19. Vitest 5s timeouts in autoCombo (#8601, #8603) reproduced on the pure origin/release/v3.8.52 tip; those files are not in this train's diff.

changelog.d/fixes/15841-haiku-5-5-adaptive-thinking.md

@@ -0,0 +1 @@
+- **fix(claude):** `claude-haiku-5-5` requests keep `thinking.type: "adaptive"` instead of being downgraded to `"enabled"`, which Anthropic rejected with HTTP 400 ([#15841](https://github.com/diegosouzapw/OmniRoute/pull/15841)) — thanks @aldoeliacim

open-sse/services/claudeHaikuConstraints.ts

@@ -1,9 +1,13 @@
+import { isAdaptiveThinkingOnly } from "../../src/shared/constants/modelSpecs.ts";
+
 type JsonRecord = Record<string, unknown>;
 
 // Models that reject `thinking.type:"adaptive"` and `output_config.effort` —
-// today, all Claude Haiku-tier models (4.5 / 3.5 / dated and aliased). Adaptive
-// thinking + the effort knob landed on Sonnet 4.6 / Opus 4.5+ only; sending
-// either on Haiku is a hard 400 from the Messages API.
+// Claude Haiku-tier models that predate adaptive thinking (4.5 / 3.5 / dated and
+// aliased). Haiku 5.5+ is adaptive-only (spec `adaptiveThinkingOnly`), so it
+// must NOT be rewritten here: the family regex alone wrongly downgrades it.
+// Adaptive thinking + the effort knob landed on Sonnet 4.6 / Opus 4.5+ and
+// Haiku 5.5; sending `enabled` to those is a hard 400 from the Messages API.
 const HAIKU_CONSTRAINT_PATTERN = /haiku/i;
 
 // Default budget when collapsing `thinking.type:"adaptive"` to a manual shape
@@ -18,6 +22,9 @@ function asRecord(value: unknown): JsonRecord | null {
 
 function modelRejectsAdaptiveAndEffort(modelId: string | null | undefined): boolean {
   if (typeof modelId !== "string" || modelId.length === 0) return false;
+  // Spec is authoritative: an adaptive-only model accepts adaptive+effort, so
+  // it is never rejected here regardless of its family name.
+  if (isAdaptiveThinkingOnly(modelId)) return false;
   return HAIKU_CONSTRAINT_PATTERN.test(modelId);
 }
 

src/shared/constants/modelSpecs.ts

@@ -417,6 +417,21 @@ export const MODEL_SPECS: Record<string, ModelSpec> = {
     aliases: BEDROCK_CLAUDE_ALIASES("claude-sonnet-5"),
   },
 
+  // ── Claude Haiku 5.5 ────────────────────────────────────────────
+  // Adaptive-thinking-only, like Sonnet 5.5: `thinking.type:"enabled"` returns
+  // 400 ("use thinking.type.adaptive and output_config.effort"). Haiku 4.5 and
+  // earlier still accept manual budgets, so this spec must NOT be widened to
+  // the /haiku/ family. Limits from the gateway catalog (context 1M, output 128K).
+  "claude-haiku-5-5": {
+    maxOutputTokens: 128000,
+    contextWindow: 1000000,
+    supportsThinking: true,
+    supportsTools: true,
+    supportsVision: true,
+    adaptiveThinkingOnly: true,
+    aliases: BEDROCK_CLAUDE_ALIASES("claude-haiku-5-5"),
+  },
+
   // ── Claude Sonnet 5.5 ───────────────────────────────────────────
   "claude-sonnet-5-5": {
     // Same shape as Sonnet 5, but it rejects thinking.type:"disabled"

tests/unit/claude-haiku-no-adaptive-thinking.test.ts

@@ -72,6 +72,30 @@ describe("normalizeClaudeHaikuConstraints", () => {
     assert.strictEqual(out, input);
   });
 
+  // Regression: Haiku 5.5 is adaptive-only (spec adaptiveThinkingOnly). The
+  // family regex used to rewrite its adaptive+effort to manual `enabled`, which
+  // Anthropic rejects with a 400 ("use thinking.type.adaptive ...").
+  it("leaves claude-haiku-5-5 adaptive thinking + effort untouched", () => {
+    const input = {
+      model: "claude-haiku-5-5",
+      thinking: { type: "adaptive" },
+      output_config: { effort: "high" },
+    };
+    const out = normalizeClaudeHaikuConstraints(input, input.model);
+    assert.strictEqual(out, input);
+    assert.deepEqual(out.thinking, { type: "adaptive" });
+    assert.deepEqual(out.output_config, { effort: "high" });
+  });
+
+  it("still downgrades adaptive on pre-5 Haiku (4.5 keeps the manual-only contract)", () => {
+    const input = {
+      model: "claude-haiku-4-5-20251001",
+      thinking: { type: "adaptive" },
+    };
+    const out = normalizeClaudeHaikuConstraints(input, input.model);
+    assert.deepEqual(out.thinking, { type: "enabled", budget_tokens: 10000 });
+  });
+
   it("leaves haiku bodies that have no adaptive thinking or effort untouched", () => {
     const input = {
       model: "claude-haiku-4-5-20251001",