Bedrock: prompt caching silently off when modelID is an application inference profile ARN #55938

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1. opencode-agent commented on Oct 16, 2026

   

   opencode-agentBot

   on Oct 16, 2026 – with OpenCode Agent

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   Thanks for the detailed report and for tracing the cause. I could reproduce this on 2.0.18, and it still happens on the latest dev (eeec76bb).

   Setup: a mock Bedrock runtime records each Converse request and counts its cachePoint blocks. OpenCode points at it through providers.amazon-bedrock.settings.baseURL, with a Claude Sonnet model and compatibility.cacheFormat: "anthropic".

   • Plain model ID: the Claude requests to /model/global.anthropic.claude-sonnet-4-5-.../converse-stream carry 2 and 4 cachePoint blocks.
   • modelID set to an application inference profile ARN: the requests to /model/arn:aws:bedrock:...:application-inference-profile/abc123/converse-stream carry 0, with or without cacheFormat: "anthropic".

   The mock can't show real cache read/write numbers, but with no cache points in the request Bedrock has nothing to cache, which fits the 0 read / 0 write you saw. As you found, BedrockCache.breakpoints() decides support only from the wire model ID, which an application profile ARN doesn't contain.

   The script below reproduces it. Related: #53756 is the same ARN problem for effort variants, and PR #53820 addresses that part only.

   Reproduction script (run.sh)

   #!/usr/bin/env bash
   # Reproduces #55938: no cachePoint blocks are sent to Bedrock when modelID is an application inference profile ARN.
   # Usage: ./run.sh            (uses `opencode` from PATH)
   #        OC_DEV=/workspace/repo ./run.sh   (runs from a source checkout)
   set -u
   DIR=$(cd "$(dirname "$0")" && pwd)
   PORT=18080
   LOG=$DIR/requests.jsonl; rm -f "$LOG"
   cat > "$DIR/mock.ts" <<'TS'
   // Mock Bedrock runtime: logs each Converse request (model in URL, cachePoint count) and returns a 400.
   const log = process.env.LOG ?? "/workspace/repro/requests.jsonl"
   Bun.serve({
     port: Number(process.env.PORT ?? 18080),
     async fetch(req) {
       const body = await req.text()
       const url = new URL(req.url)
       const cachePoints = (body.match(/"cachePoint"/g) ?? []).length
       await Bun.write(log, (await Bun.file(log).text().catch(() => "")) + JSON.stringify({ path: decodeURIComponent(url.pathname), cachePoints }) + "\n")
       return new Response(JSON.stringify({ message: "mock: stop here" }), { status: 400, headers: { "content-type": "application/json", "x-amzn-errortype": "ValidationException" } })
     },
   })
   TS
   LOG=$LOG PORT=$PORT bun "$DIR/mock.ts" & MOCK=$!; sleep 1
   if [ -n "${OC_DEV:-}" ]; then
     # the standalone server child is spawned without these flags, so pass them via BUN_OPTIONS too
     export BUN_OPTIONS="--conditions=browser --preload=$OC_DEV/packages/tui/node_modules/@opentui/solid/scripts/preload.js"
     OC=(bun --conditions=browser --preload="$OC_DEV/packages/tui/node_modules/@opentui/solid/scripts/preload.js" "$OC_DEV/packages/cli/src/index.ts")
   else OC=(opencode); fi
   for MODE in plain arn; do
     P=$(mktemp -d); export HOME=$P/home XDG_CONFIG_HOME=$P/home/.config XDG_DATA_HOME=$P/home/.data XDG_STATE_HOME=$P/home/.state XDG_CACHE_HOME=$P/home/.cache
     mkdir -p "$HOME"; cd "$P"; git init -q
     if [ $MODE = arn ]; then MID='"modelID": "arn:aws:bedrock:us-east-1:123456789012:application-inference-profile/abc123",'; else MID=''; fi
     cat > opencode.jsonc <<JSON
   {
     "providers": {
       "amazon-bedrock": {
         "settings": { "baseURL": "http://127.0.0.1:$PORT", "apiKey": "dummy", "region": "us-east-1" },
         "models": {
           "global.anthropic.claude-sonnet-4-5-20250929-v1:0": { $MID "compatibility": { "cacheFormat": "anthropic" } }
         }
       }
     }
   }
   JSON
     echo "== $MODE"
     echo "{\"mode\":\"$MODE\"}" >> "$LOG"
     AWS_BEARER_TOKEN_BEDROCK=dummy timeout 60 "${OC[@]}" run --standalone --format json --model "amazon-bedrock/global.anthropic.claude-sonnet-4-5-20250929-v1:0" "hello" 2>&1 | tail -3
   done
   kill $MOCK
   echo "== requests seen by mock Bedrock"; cat "$LOG"

   Run it: bash run.sh
2. opencode-agent

   added

   reproduced

   on Oct 16, 2026
3. rekram1-node

   closed this as completedin #55942on Oct 16, 2026