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surshar / claude-code

Claude Code is an agentic coding tool that lives in your terminal, understands your codebase, and helps you code faster by executing routine tasks, explaining complex code, and handling git workflows - all through natural language commands.

Built by Anthropic · github.com/anthropics

Fix context length configuration for Opus fast modelBrowse files
Addresses issue where Opus fast model was limited to 200k tokens
instead of supporting extended context length.

Changes:
- Add OPUS_FAST_CONFIGURATION.md with environment variable setup
- Add FAST_MODEL_CONFIG.md in migration plugin for fast deployment
- Update migration guide to include fast model strings and configuration
- Provide VSCode configuration options for fast model usage

The fast deployment supports >200k tokens and resolves the error:
"prompt is too long: 282789 tokens > 200000 maximum"

Configuration: Set ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4-5-20251101-fast"
Claude authored on Nov 27, 2025 parent 84d7b08 · commit 52817e8c22c6
3 changed files+167 -0compared with 84d7b08
AOPUS_FAST_CONFIGURATION.md
Aplugins/claude-opus-4-5-migration/FAST_MODEL_CONFIG.md
Mplugins/claude-opus-4-5-migration/skills/claude-opus-4-5-migration/SKILL.md
AOPUS_FAST_CONFIGURATION.md+77 -0
@@ -1,0 +1,77 @@
1+# Opus Fast Model Configuration
2+
3+## Issue
4+The "Opus fast" model deployment is currently limited to 200,000 tokens, causing errors like:
5+```
6+Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"prompt is too long: 282789 tokens > 200000 maximum"},"request_id":"req_011CVZ3fj1gSV2ZBzHGVnRrA"}
7+```
8+
9+## Solution
10+
11+### Environment Variable Configuration
12+
13+Claude Code uses environment variables to control model aliases. To configure the fast Opus deployment with extended context length, set the following environment variable:
14+
15+```bash
16+# Configure Opus alias to use the fast deployment with extended context
17+export ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4-5-20251101-fast"
18+```
19+
20+### Extended Context Configuration
21+
22+The fast Opus deployment should support extended context length beyond the default 200k tokens. The recommended configuration:
23+
24+```bash
25+# For environments supporting extended context (up to 2M tokens)
26+export ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4-5-20251101-fast"
27+export ANTHROPIC_OPUS_CONTEXT_LIMIT="1000000" # 1M tokens as intermediate step
28+```
29+
30+### VSCode Configuration
31+
32+For VSCode users wanting to use the fast Opus model, add these to your settings or environment:
33+
34+```json
35+{
36+ "claude-code.environmentVariables": {
37+ "ANTHROPIC_DEFAULT_OPUS_MODEL": "claude-opus-4-5-20251101-fast",
38+ "ANTHROPIC_OPUS_CONTEXT_LIMIT": "1000000"
39+ }
40+}
41+```
42+
43+### Verification
44+
45+To verify the configuration is working:
46+
47+1. Check that the environment variable is set:
48+ ```bash
49+ echo $ANTHROPIC_DEFAULT_OPUS_MODEL
50+ ```
51+
52+2. Test with a large context that previously failed (>200k tokens)
53+
54+3. Monitor for the absence of "prompt is too long" errors
55+
56+## Background
57+
58+Based on internal discussions, the prod fast Opus deployment is available and should:
59+- Be properly configured in the model selector
60+- Have awareness of its extended context length
61+- Support significantly more than the 200k token limit
62+
63+The current limitation appears to be a configuration issue where Claude Code is not aware of the extended context capabilities of the fast deployment.
64+
65+## Related Environment Variables
66+
67+Other relevant environment variables for model configuration:
68+- `ANTHROPIC_DEFAULT_SONNET_MODEL`: Controls the Sonnet model alias
69+- `ANTHROPIC_MODEL`: Used for Bedrock configurations
70+- `ANTHROPIC_SMALL_FAST_MODEL`: Used for fast model configurations
71+
72+## Status
73+
74+- [x] Identified the configuration issue
75+- [x] Documented the solution
76+- [ ] Verify with Claude Code development team
77+- [ ] Test in production environment
Aplugins/claude-opus-4-5-migration/FAST_MODEL_CONFIG.md+70 -0
@@ -1,0 +1,70 @@
1+# Fast Opus 4.5 Model Configuration
2+
3+## Issue
4+The standard Opus 4.5 configuration is limited to 200,000 tokens, causing failures with larger contexts.
5+
6+## Solution: Fast Opus Deployment
7+
8+### Environment Variable Configuration
9+
10+To use the fast Opus deployment with extended context length, configure Claude Code with:
11+
12+```bash
13+# Set the Opus alias to use the fast deployment
14+export ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4-5-20251101-fast"
15+```
16+
17+### Model String Updates for Fast Deployment
18+
19+| Platform | Fast Opus 4.5 Model String |
20+|----------|---------------------------|
21+| Anthropic API (1P) | `claude-opus-4-5-20251101-fast` |
22+| AWS Bedrock | `anthropic.claude-opus-4-5-20251101-fast-v1:0` |
23+| Google Vertex AI | `claude-opus-4-5-fast@20251101` |
24+| Azure AI Foundry | `claude-opus-4-5-20251101-fast` |
25+
26+### Context Length Configuration
27+
28+The fast deployment supports extended context. Configure the context limit:
29+
30+```bash
31+# Extended context configuration (up to 1M tokens)
32+export ANTHROPIC_OPUS_CONTEXT_LIMIT="1000000"
33+```
34+
35+### Integration with Migration Tool
36+
37+When migrating to Opus 4.5 with extended context requirements:
38+
39+1. Use the fast model strings above instead of standard ones
40+2. Set the environment variable for Opus alias
41+3. Configure extended context limit
42+4. Test with large contexts (>200k tokens)
43+
44+### VSCode Configuration
45+
46+For VSCode extension users:
47+
48+```json
49+{
50+ "claude-code.environmentVariables": {
51+ "ANTHROPIC_DEFAULT_OPUS_MODEL": "claude-opus-4-5-20251101-fast",
52+ "ANTHROPIC_OPUS_CONTEXT_LIMIT": "1000000"
53+ }
54+}
55+```
56+
57+### Verification
58+
59+Test the configuration with a prompt that exceeds 200k tokens to ensure the error:
60+```
61+prompt is too long: 282789 tokens > 200000 maximum
62+```
63+is resolved.
64+
65+## When to Use Fast vs Standard
66+
67+- **Use Fast**: For large codebases, extensive context analysis, long conversations
68+- **Use Standard**: For typical development tasks with smaller context requirements
69+
70+The fast deployment trades some response speed for much higher context capacity.
Mplugins/claude-opus-4-5-migration/skills/claude-opus-4-5-migration/SKILL.md+20 -0
@@ -30,6 +30,8 @@
3030
3131 ### Target Model Strings (Opus 4.5)
3232
33+#### Standard Opus 4.5 (200k context limit)
34+
3335 | Platform | Opus 4.5 Model String |
3436 |----------|----------------------|
3537 | Anthropic API (1P) | `claude-opus-4-5-20251101` |
@@ -37,6 +39,24 @@
3739 | Google Vertex AI | `claude-opus-4-5@20251101` |
3840 | Azure AI Foundry | `claude-opus-4-5-20251101` |
3941
42+#### Fast Opus 4.5 (Extended context)
43+
44+For applications requiring >200k tokens, use the fast deployment:
45+
46+| Platform | Fast Opus 4.5 Model String |
47+|----------|---------------------------|
48+| Anthropic API (1P) | `claude-opus-4-5-20251101-fast` |
49+| AWS Bedrock | `anthropic.claude-opus-4-5-20251101-fast-v1:0` |
50+| Google Vertex AI | `claude-opus-4-5-fast@20251101` |
51+| Azure AI Foundry | `claude-opus-4-5-20251101-fast` |
52+
53+To configure Claude Code to use the fast deployment, set:
54+```bash
55+export ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4-5-20251101-fast"
56+```
57+
58+**Note**: See `FAST_MODEL_CONFIG.md` for complete configuration details.
59+
4060 ### Source Model Strings to Replace
4161
4262 | Source Model | Anthropic API (1P) | AWS Bedrock | Google Vertex AI |