diff --git a/go.mod b/go.mod
index 8bcc9c7a4a..f9dd04d8bd 100644
--- a/go.mod
+++ b/go.mod
@@ -81,13 +81,14 @@ replace github.com/spf13/afero => github.com/aslilac/afero v0.0.0-20250403163713
 // 2) Go 1.25 downgrade for Windows CI compat
 // 3) ibetitsmike/fantasy#4 — skip ephemeral replay items when store=false
 // 4) (anthropic-sdk-go) dannykopping's appendCompact performance fixes
-// See: https://github.com/coder/fantasy/commits/7aaf56df81f9
-replace charm.land/fantasy => github.com/coder/fantasy v0.0.0-20260409111551-7aaf56df81f9
+// 5) (anthropic-sdk-go) DirectEncoder to eliminate nested MarshalJSON allocation chain
+// See: https://github.com/coder/fantasy/commits/190272ce52f0
+replace charm.land/fantasy => github.com/coder/fantasy v0.0.0-20260415162245-190272ce52f0
 
 // coder/coder uses a fork of charmbracelet's fork of the Anthropic Go SDK with some
 // additional performance improvements.
-// See: https://github.com/coder/anthropic-sdk-go/commits/5711db120546
-replace github.com/charmbracelet/anthropic-sdk-go => github.com/coder/anthropic-sdk-go v0.0.0-20260409105508-5711db120546
+// See: https://github.com/coder/anthropic-sdk-go/commits/a31d7d0e7067
+replace github.com/charmbracelet/anthropic-sdk-go => github.com/coder/anthropic-sdk-go v0.0.0-20260415160422-a31d7d0e7067
 
 // Replace sdks with our own optimized forks until relevant upstream PRs are merged.
 // https://github.com/anthropics/anthropic-sdk-go/pull/262
diff --git a/go.sum b/go.sum
index 463339c3ec..2391296fda 100644
--- a/go.sum
+++ b/go.sum
@@ -316,16 +316,16 @@ github.com/coder/aibridge v1.1.2 h1:DLz0B7j9qzGj/nVQUbWDluux2c/y7+a7xGgc+63uOUM=
 github.com/coder/aibridge v1.1.2/go.mod h1:k2/JzBF/jW2h4xKYyXXy9gbD7qaf0kKvfXxwA2JCYxE=
 github.com/coder/aisdk-go v0.0.9 h1:Vzo/k2qwVGLTR10ESDeP2Ecek1SdPfZlEjtTfMveiVo=
 github.com/coder/aisdk-go v0.0.9/go.mod h1:KF6/Vkono0FJJOtWtveh5j7yfNrSctVTpwgweYWSp5M=
-github.com/coder/anthropic-sdk-go v0.0.0-20260409105508-5711db120546 h1:dYAA1uo93n9r/B4Gvx76pjaeS0kBTX1lO0WX0p0uqo8=
-github.com/coder/anthropic-sdk-go v0.0.0-20260409105508-5711db120546/go.mod h1:hqlYqR7uPKOKfnNeicUbZp0Ps0GeYFlKYtwh5HGDCx8=
+github.com/coder/anthropic-sdk-go v0.0.0-20260415160422-a31d7d0e7067 h1:v1RAkUO21u0QH6UlUueSHMbgFf++BZZW41Rj6LM2eWo=
+github.com/coder/anthropic-sdk-go v0.0.0-20260415160422-a31d7d0e7067/go.mod h1:hqlYqR7uPKOKfnNeicUbZp0Ps0GeYFlKYtwh5HGDCx8=
 github.com/coder/boundary v0.8.4-0.20260304164748-566aeea939ab h1:HrlxyTmMQpOHfSKzRU1vf5TxrmV6vL5OiWq+Dvn5qh0=
 github.com/coder/boundary v0.8.4-0.20260304164748-566aeea939ab/go.mod h1:BhJhyKW/+zZQzaGZ3vn27if2k0Vx5xLXzq7ZCQx5gPk=
 github.com/coder/bubbletea v1.2.2-0.20241212190825-007a1cdb2c41 h1:SBN/DA63+ZHwuWwPHPYoCZ/KLAjHv5g4h2MS4f2/MTI=
 github.com/coder/bubbletea v1.2.2-0.20241212190825-007a1cdb2c41/go.mod h1:I9ULxr64UaOSUv7hcb3nX4kowodJCVS7vt7VVJk/kW4=
 github.com/coder/clistat v1.2.1 h1:P9/10njXMyj5cWzIU5wkRsSy5LVQH49+tcGMsAgWX0w=
 github.com/coder/clistat v1.2.1/go.mod h1:m7SC0uj88eEERgvF8Kn6+w6XF21BeSr+15f7GoLAw0A=
-github.com/coder/fantasy v0.0.0-20260409111551-7aaf56df81f9 h1:cElc6pUurkUNX2pOO1/QxiglXrOEZHVNiRFbNyW6YqQ=
-github.com/coder/fantasy v0.0.0-20260409111551-7aaf56df81f9/go.mod h1:1h1Wp83HWOkLHhIFFQYVNBry07dtkqs+Xsm14oawHSY=
+github.com/coder/fantasy v0.0.0-20260415162245-190272ce52f0 h1:qv8PhuP2tbbR/CR3qnbLWwf+zn/nD+8LcQMWrktxZcQ=
+github.com/coder/fantasy v0.0.0-20260415162245-190272ce52f0/go.mod h1:wZ0e3lEPqrM0XiIdAUQLvMKCLYhc3gi96MRX2wjbX44=
 github.com/coder/flog v1.1.0 h1:kbAes1ai8fIS5OeV+QAnKBQE22ty1jRF/mcAwHpLBa4=
 github.com/coder/flog v1.1.0/go.mod h1:UQlQvrkJBvnRGo69Le8E24Tcl5SJleAAR7gYEHzAmdQ=
 github.com/coder/go-httpstat v0.0.0-20230801153223-321c88088322 h1:m0lPZjlQ7vdVpRBPKfYIFlmgevoTkBxB10wv6l2gOaU=