docs: add variable substitution behavior documentation for sessions and chat #877
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…nd chat Explains how variableValues work when using sessions with the Chat API: - Variables are substituted at session creation and "baked in" - Subsequent chat requests cannot override with new variableValues - Fresh templates must be provided to use different values Includes code examples, quick reference table, and best practices. VAP-11219 Co-Authored-By: Claude <noreply@anthropic.com>
VAP-11219 Co-Authored-By: Claude <noreply@anthropic.com>
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- Changed all examples from gpt-4o-mini to gpt-4.1
- Added note explaining that Vapi uses LiquidJS for variable substitution
- Clarified that {{ }} syntax follows Liquid template language conventions
VAP-11219
Co-Authored-By: Claude <noreply@anthropic.com>
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🌿 Preview your docs: https://vapi-preview-71aede7e-ac42-48aa-bd62-e224b4fc2586.docs.buildwithfern.com |
Remove TypeScript and Python code examples, keeping only cURL for cleaner documentation. VAP-11219 Co-Authored-By: Claude <noreply@anthropic.com>
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🌿 Preview your docs: https://vapi-preview-8afac9b4-d6a2-49b8-ad33-37c41b92b209.docs.buildwithfern.com |
Replace placeholder IDs with proper UUID format examples. VAP-11219 Co-Authored-By: Claude <noreply@anthropic.com>
stevenbdf
approved these changes
Jan 15, 2026
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Summary
fern/chat/variable-substitution.mdx) explaining howvariableValuesbehave when using sessions with the Chat APIfern/docs.ymlto add the new page to the Chat section navigationWhat this documents
This page explains a critical behavior that developers need to understand:
assistantOverrides.variableValuesinPOST /session, the template placeholders (e.g.,{{name}}) are immediately substituted and the pre-substituted assistant is storedsessionIdautomatically use the stored values{{}}placeholders no longer exist in the stored assistant{{}}placeholders along with newvariableValuesContent includes
Test plan
Closes VAP-11219
🤖 Generated with Claude Code