diff --git a/go/ql/lib/ext/context.model.yml b/go/ql/lib/ext/context.model.yml
index b71adeb6b3c7..5df5cb6d6295 100644
--- a/go/ql/lib/ext/context.model.yml
+++ b/go/ql/lib/ext/context.model.yml
@@ -3,8 +3,14 @@ extensions:
       pack: codeql/go-all
       extensible: summaryModel
     data:
+      # AfterFunc should be modeled when callback-based library models are supported.
       - ["context", "", False, "WithCancel", "", "", "Argument[0]", "ReturnValue[0]", "taint", "manual"]
       - ["context", "", False, "WithDeadline", "", "", "Argument[0]", "ReturnValue[0]", "taint", "manual"]
+      - ["context", "", False, "WithDeadlineCause", "", "", "Argument[0]", "ReturnValue[0]", "taint", "manual"]
+      - ["context", "", False, "WithDeadlineCause", "", "", "Argument[2]", "ReturnValue[0]", "taint", "manual"]
       - ["context", "", False, "WithTimeout", "", "", "Argument[0]", "ReturnValue[0]", "taint", "manual"]
+      - ["context", "", False, "WithTimeoutCause", "", "", "Argument[0]", "ReturnValue[0]", "taint", "manual"]
+      - ["context", "", False, "WithTimeoutCause", "", "", "Argument[2]", "ReturnValue[0]", "taint", "manual"]
       - ["context", "", False, "WithValue", "", "", "Argument[0..2]", "ReturnValue", "taint", "manual"]
+      - ["context", "", False, "WithoutCancel", "", "", "Argument[0]", "ReturnValue", "taint", "manual"]
       - ["context", "Context", True, "Value", "", "", "Argument[receiver]", "ReturnValue", "taint", "manual"]
diff --git a/go/ql/lib/ext/crypto.tls.model.yml b/go/ql/lib/ext/crypto.tls.model.yml
index ecb4c8859946..6ec868eebed8 100644
--- a/go/ql/lib/ext/crypto.tls.model.yml
+++ b/go/ql/lib/ext/crypto.tls.model.yml
@@ -4,5 +4,19 @@ extensions:
       extensible: summaryModel
     data:
       - ["crypto/tls", "", False, "Client", "", "", "Argument[0]", "ReturnValue", "taint", "manual"]
+      - ["crypto/tls", "", False, "NewResumptionState", "", "", "Argument[0..1]", "ReturnValue[0]", "taint", "manual"]
       - ["crypto/tls", "", False, "NewListener", "", "", "Argument[0]", "ReturnValue", "taint", "manual"]
+      - ["crypto/tls", "", False, "ParseSessionState", "", "", "Argument[0]", "ReturnValue[0]", "taint", "manual"]
+      - ["crypto/tls", "", False, "QUICClient", "", "", "Argument[0]", "ReturnValue", "taint", "manual"]
+      - ["crypto/tls", "", False, "QUICServer", "", "", "Argument[0]", "ReturnValue", "taint", "manual"]
       - ["crypto/tls", "", False, "Server", "", "", "Argument[0]", "ReturnValue", "taint", "manual"]
+      - ["crypto/tls", "ClientSessionState", True, "ResumptionState", "", "", "Argument[receiver]", "ReturnValue[0..1]", "taint", "manual"]
+      - ["crypto/tls", "Config", True, "DecryptTicket", "", "", "Argument[receiver]", "ReturnValue[0]", "taint", "manual"]
+      - ["crypto/tls", "Config", True, "DecryptTicket", "", "", "Argument[0..1]", "ReturnValue[0]", "taint", "manual"]
+      - ["crypto/tls", "Config", True, "EncryptTicket", "", "", "Argument[receiver]", "ReturnValue[0]", "taint", "manual"]
+      - ["crypto/tls", "Config", True, "EncryptTicket", "", "", "Argument[0..1]", "ReturnValue[0]", "taint", "manual"]
+      - ["crypto/tls", "QUICConn", True, "ConnectionState", "", "", "Argument[receiver]", "ReturnValue", "taint", "manual"]
+      - ["crypto/tls", "QUICConn", True, "HandleData", "", "", "Argument[1]", "Argument[receiver]", "taint", "manual"]
+      - ["crypto/tls", "QUICConn", True, "NextEvent", "", "", "Argument[receiver]", "ReturnValue", "taint", "manual"]
+      - ["crypto/tls", "QUICConn", True, "SetTransportParameters", "", "", "Argument[0]", "Argument[receiver]", "taint", "manual"]
+      - ["crypto/tls", "SessionState", True, "Bytes", "", "", "Argument[receiver]", "ReturnValue[0]", "taint", "manual"]
diff --git a/go/ql/lib/ext/io.fs.model.yml b/go/ql/lib/ext/io.fs.model.yml
index 1b9be01aba91..6d8c14253dda 100644
--- a/go/ql/lib/ext/io.fs.model.yml
+++ b/go/ql/lib/ext/io.fs.model.yml
@@ -4,6 +4,8 @@ extensions:
       extensible: summaryModel
     data:
       - ["io/fs", "", False, "FileInfoToDirEntry", "", "", "Argument[0]", "ReturnValue", "taint", "manual"]
+      - ["io/fs", "", False, "FormatDirEntry", "", "", "Argument[0]", "ReturnValue", "taint", "manual"]
+      - ["io/fs", "", False, "FormatFileInfo", "", "", "Argument[0]", "ReturnValue", "taint", "manual"]
       - ["io/fs", "", False, "Glob", "", "", "Argument[0]", "ReturnValue[0]", "taint", "manual"]
       - ["io/fs", "", False, "ReadDir", "", "", "Argument[0]", "ReturnValue[0]", "taint", "manual"]
       - ["io/fs", "", False, "ReadFile", "", "", "Argument[0]", "ReturnValue[0]", "taint", "manual"]
diff --git a/go/ql/lib/ext/math.big.model.yml b/go/ql/lib/ext/math.big.model.yml
index dc09561897c9..1f7ff4ee8c08 100644
--- a/go/ql/lib/ext/math.big.model.yml
+++ b/go/ql/lib/ext/math.big.model.yml
@@ -3,4 +3,5 @@ extensions:
       pack: codeql/go-all
       extensible: summaryModel
     data:
+      - ["math/big", "Int", True, "Float64", "", "", "Argument[receiver]", "ReturnValue[0]", "taint", "manual"]
       - ["math/big", "Int", True, "Int64", "", "", "Argument[receiver]", "ReturnValue[0]", "taint", "manual"]
diff --git a/go/ql/src/change-notes/2026-09-30-model-go1.21-minor-library-changes.md b/go/ql/src/change-notes/2026-09-30-model-go1.21-minor-library-changes.md
new file mode 100644
index 000000000000..38fcf403bb04
--- /dev/null
+++ b/go/ql/src/change-notes/2026-09-30-model-go1.21-minor-library-changes.md
@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Added data flow models for APIs mentioned in the minor library changes section of the Go 1.21 release notes.
diff --git a/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/Context.go b/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/Context.go
index 5b526f3b8c0a..bce42b1ca3fa 100644
--- a/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/Context.go
+++ b/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/Context.go
@@ -26,6 +26,35 @@ func TaintStepTest_ContextWithTimeout_B0I0O0(sourceCQL interface{}) interface{}
 	return intoContext957
 }
 
+func TaintStepTest_ContextWithDeadlineCauseContext(sourceCQL interface{}) interface{} {
+	fromContext := sourceCQL.(context.Context)
+	intoContext, _ := context.WithDeadlineCause(fromContext, time.Time{}, nil)
+	return intoContext
+}
+
+func TaintStepTest_ContextWithDeadlineCauseError(sourceCQL interface{}) interface{} {
+	fromError := sourceCQL.(error)
+	intoContext, _ := context.WithDeadlineCause(nil, time.Time{}, fromError)
+	return intoContext
+}
+
+func TaintStepTest_ContextWithTimeoutCauseContext(sourceCQL interface{}) interface{} {
+	fromContext := sourceCQL.(context.Context)
+	intoContext, _ := context.WithTimeoutCause(fromContext, 0, nil)
+	return intoContext
+}
+
+func TaintStepTest_ContextWithTimeoutCauseError(sourceCQL interface{}) interface{} {
+	fromError := sourceCQL.(error)
+	intoContext, _ := context.WithTimeoutCause(nil, 0, fromError)
+	return intoContext
+}
+
+func TaintStepTest_ContextWithoutCancel(sourceCQL interface{}) interface{} {
+	fromContext := sourceCQL.(context.Context)
+	return context.WithoutCancel(fromContext)
+}
+
 func TaintStepTest_ContextWithValue_B0I0O0(sourceCQL interface{}) interface{} {
 	fromContext520 := sourceCQL.(context.Context)
 	intoContext443 := context.WithValue(fromContext520, nil, nil)
@@ -163,4 +192,29 @@ func RunAllTaints_Context() {
 		out := TaintStepTest_OldContextContextValue_B0I0O0(source)
 		sink(13, out)
 	}
+	{
+		source := newSource(14)
+		out := TaintStepTest_ContextWithDeadlineCauseContext(source)
+		sink(14, out)
+	}
+	{
+		source := newSource(15)
+		out := TaintStepTest_ContextWithDeadlineCauseError(source)
+		sink(15, out)
+	}
+	{
+		source := newSource(16)
+		out := TaintStepTest_ContextWithTimeoutCauseContext(source)
+		sink(16, out)
+	}
+	{
+		source := newSource(17)
+		out := TaintStepTest_ContextWithTimeoutCauseError(source)
+		sink(17, out)
+	}
+	{
+		source := newSource(18)
+		out := TaintStepTest_ContextWithoutCancel(source)
+		sink(18, out)
+	}
 }
diff --git a/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/CryptoTls.go b/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/CryptoTls.go
index a35f30a1a991..2a5c81c651f0 100644
--- a/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/CryptoTls.go
+++ b/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/CryptoTls.go
@@ -55,6 +55,71 @@ func TaintStepTest_CryptoTlsConnWrite_B0I0O0(sourceCQL interface{}) interface{}
 	return intoConn584
 }
 
+func TaintStepTest_CryptoTlsSessionStateBytes(sourceCQL interface{}) interface{} {
+	out, _ := sourceCQL.(*tls.SessionState).Bytes()
+	return out
+}
+
+func TaintStepTest_CryptoTlsParseSessionState(sourceCQL interface{}) interface{} {
+	out, _ := tls.ParseSessionState(sourceCQL.([]byte))
+	return out
+}
+
+func TaintStepTest_CryptoTlsNewResumptionStateTicket(sourceCQL interface{}) interface{} {
+	out, _ := tls.NewResumptionState(sourceCQL.([]byte), nil)
+	return out
+}
+
+func TaintStepTest_CryptoTlsNewResumptionStateState(sourceCQL interface{}) interface{} {
+	out, _ := tls.NewResumptionState(nil, sourceCQL.(*tls.SessionState))
+	return out
+}
+
+func TaintStepTest_CryptoTlsClientSessionStateResumptionState(sourceCQL interface{}) interface{} {
+	ticket, _, _ := sourceCQL.(*tls.ClientSessionState).ResumptionState()
+	return ticket
+}
+
+func TaintStepTest_CryptoTlsConfigEncryptTicketState(sourceCQL interface{}) interface{} {
+	var config tls.Config
+	out, _ := config.EncryptTicket(tls.ConnectionState{}, sourceCQL.(*tls.SessionState))
+	return out
+}
+
+func TaintStepTest_CryptoTlsConfigDecryptTicket(sourceCQL interface{}) interface{} {
+	var config tls.Config
+	out, _ := config.DecryptTicket(sourceCQL.([]byte), tls.ConnectionState{})
+	return out
+}
+
+func TaintStepTest_CryptoTlsQUICClient(sourceCQL interface{}) interface{} {
+	return tls.QUICClient(sourceCQL.(*tls.QUICConfig))
+}
+
+func TaintStepTest_CryptoTlsQUICServer(sourceCQL interface{}) interface{} {
+	return tls.QUICServer(sourceCQL.(*tls.QUICConfig))
+}
+
+func TaintStepTest_CryptoTlsQUICConnHandleData(sourceCQL interface{}) interface{} {
+	conn := tls.QUICClient(&tls.QUICConfig{})
+	conn.HandleData(tls.QUICEncryptionLevelInitial, sourceCQL.([]byte))
+	return conn
+}
+
+func TaintStepTest_CryptoTlsQUICConnNextEvent(sourceCQL interface{}) interface{} {
+	return sourceCQL.(*tls.QUICConn).NextEvent()
+}
+
+func TaintStepTest_CryptoTlsQUICConnConnectionState(sourceCQL interface{}) interface{} {
+	return sourceCQL.(*tls.QUICConn).ConnectionState()
+}
+
+func TaintStepTest_CryptoTlsQUICConnSetTransportParameters(sourceCQL interface{}) interface{} {
+	conn := tls.QUICClient(&tls.QUICConfig{})
+	conn.SetTransportParameters(sourceCQL.([]byte))
+	return conn
+}
+
 func RunAllTaints_CryptoTls() {
 	{
 		source := newSource(0)
@@ -91,4 +156,69 @@ func RunAllTaints_CryptoTls() {
 		out := TaintStepTest_CryptoTlsConnWrite_B0I0O0(source)
 		sink(6, out)
 	}
+	{
+		source := newSource(8)
+		out := TaintStepTest_CryptoTlsSessionStateBytes(source)
+		sink(8, out)
+	}
+	{
+		source := newSource(9)
+		out := TaintStepTest_CryptoTlsParseSessionState(source)
+		sink(9, out)
+	}
+	{
+		source := newSource(10)
+		out := TaintStepTest_CryptoTlsNewResumptionStateTicket(source)
+		sink(10, out)
+	}
+	{
+		source := newSource(11)
+		out := TaintStepTest_CryptoTlsNewResumptionStateState(source)
+		sink(11, out)
+	}
+	{
+		source := newSource(12)
+		out := TaintStepTest_CryptoTlsClientSessionStateResumptionState(source)
+		sink(12, out)
+	}
+	{
+		source := newSource(13)
+		out := TaintStepTest_CryptoTlsConfigEncryptTicketState(source)
+		sink(13, out)
+	}
+	{
+		source := newSource(14)
+		out := TaintStepTest_CryptoTlsConfigDecryptTicket(source)
+		sink(14, out)
+	}
+	{
+		source := newSource(15)
+		out := TaintStepTest_CryptoTlsQUICClient(source)
+		sink(15, out)
+	}
+	{
+		source := newSource(16)
+		out := TaintStepTest_CryptoTlsQUICServer(source)
+		sink(16, out)
+	}
+	{
+		source := newSource(17)
+		out := TaintStepTest_CryptoTlsQUICConnHandleData(source)
+		sink(17, out)
+	}
+	{
+		source := newSource(18)
+		out := TaintStepTest_CryptoTlsQUICConnNextEvent(source)
+		sink(18, out)
+	}
+	{
+		source := newSource(19)
+		out := TaintStepTest_CryptoTlsQUICConnConnectionState(source)
+		sink(19, out)
+	}
+	{
+		source := newSource(20)
+		out := TaintStepTest_CryptoTlsQUICConnSetTransportParameters(source)
+		sink(20, out)
+	}
 }
diff --git a/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/IoFs.go b/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/IoFs.go
index 4b9102008413..e6db16aee2e0 100644
--- a/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/IoFs.go
+++ b/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/IoFs.go
@@ -11,6 +11,16 @@ func walkDirCallback(path string, d fs.DirEntry, _ error) error {
 }
 
 func steps() {
+	{
+		source := newSource(17).(fs.DirEntry)
+		out := fs.FormatDirEntry(source)
+		sink(17, out)
+	}
+	{
+		source := newSource(18).(fs.FileInfo)
+		out := fs.FormatFileInfo(source)
+		sink(18, out)
+	}
 	{
 		source := newSource(16).(fs.FileInfo)
 		out := fs.FileInfoToDirEntry(source)
diff --git a/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/MathBig.go b/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/MathBig.go
new file mode 100644
index 000000000000..0be95bb7b223
--- /dev/null
+++ b/go/ql/test/library-tests/semmle/go/frameworks/StdlibTaintFlow/MathBig.go
@@ -0,0 +1,14 @@
+package main
+
+import "math/big"
+
+func TaintStepTest_MathBigIntFloat64(sourceCQL interface{}) interface{} {
+	out, _ := sourceCQL.(*big.Int).Float64()
+	return out
+}
+
+func RunAllTaints_MathBig() {
+	source := newSource(0)
+	out := TaintStepTest_MathBigIntFloat64(source)
+	sink(0, out)
+}