diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index fc605243..f3a72add 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added opt-in faux provider helpers for deterministic tests and scripted demos: `registerFauxProvider()`, `fauxAssistantMessage()`, `fauxText()`, `fauxThinking()`, and `fauxToolCall()`.
+
 ## [0.63.2] - 2026-03-29
 
 ## [0.63.1] - 2026-03-27
diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 3253a2d4..4d9064a2 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Breaking Changes
+
+- `ModelRegistry` no longer has a public constructor. SDK callers and tests must use `ModelRegistry.create(authStorage, modelsJsonPath?)` for file-backed registries or `ModelRegistry.inMemory(authStorage)` for built-in-only registries. Direct `new ModelRegistry(...)` calls no longer compile.
+
 ### Added
 
 - Added `ToolDefinition.prepareArguments` hook to prepare raw tool call arguments before schema validation, enabling compatibility shims for resumed sessions with outdated tool schemas