diff --git a/pkg/addons/contract/connector.go b/pkg/addons/contract/connector.go
index 0232931cd7..5e86d642d9 100644
--- a/pkg/addons/contract/connector.go
+++ b/pkg/addons/contract/connector.go
@@ -23,8 +23,9 @@ import (
 //     the add-on calls the host operation ConnectorInboundOp.
 //   - Outbound. The host calls "/connector" with the ops "send", "edit",
 //     "typing", "send_file" and "me", "media" to read a file a message
-//     carries, and "draft" for a kind that declares drafts. The host passes
-//     the token on every call; the add-on never stores it.
+//     carries, "draft" for a kind that declares drafts and "history" for a
+//     kind that declares history. The host passes the token on every call;
+//     the add-on never stores it.
 
 // Delivery says how messages reach the host.
 const (
@@ -55,6 +56,10 @@ const (
 	// that is not a message yet. The platform replaces it when the answer
 	// is sent. Only a kind with Drafts serves it.
 	ConnectorOpDraft = "draft"
+	// ConnectorOpHistory returns the earlier messages of the thread
+	// ConnectorRequest.Thread of Chat, oldest first. Only a kind with
+	// History serves it; the host never calls it for another kind.
+	ConnectorOpHistory = "history"
 )
 
 // Codes of a ConnectorError.
@@ -89,6 +94,17 @@ const (
 	// MinPreviewMs and MaxPreviewMs bound ConnectorKind.PreviewMs.
 	MinPreviewMs = 250
 	MaxPreviewMs = 10000
+	// MinHistoryAPI is the first manifest API version that knows the History
+	// ability of a connector kind.
+	MinHistoryAPI uint64 = 2
+	// DefaultHistoryMessages is how many messages the host asks the op
+	// history for when the kind declares no limit of its own.
+	DefaultHistoryMessages = 30
+	// MaxHistoryMessages bounds ConnectorHistory.MaxMessages and the Limit of
+	// a history request.
+	MaxHistoryMessages = 200
+	// MaxHistoryMedia is how many file names one history message carries.
+	MaxHistoryMedia = 8
 )
 
 // ConnectorKind is one kind of binding an add-on serves, such as telegram.
@@ -114,6 +130,35 @@ type ConnectorKind struct {
 	// of an answer (an edit or a draft) of one binding. Zero: the host's
 	// default, one second. Else MinPreviewMs to MaxPreviewMs.
 	PreviewMs int `json:"previewMs,omitempty"`
+	// History declares that the add-on serves the op history. A kind without
+	// it keeps the behaviour of a platform that cannot be asked for old
+	// messages. It needs manifest api MinHistoryAPI.
+	History *ConnectorHistory `json:"history,omitempty"`
+}
+
+// ConnectorHistory is the ability to read old messages of a platform.
+type ConnectorHistory struct {
+	// Thread says that the op history returns the earlier messages of a
+	// thread. It must be true: it is the only ability so far.
+	Thread bool `json:"thread"`
+	// MaxMessages is the most messages one call returns. Zero: the host
+	// asks for DefaultHistoryMessages. At most MaxHistoryMessages.
+	MaxMessages int `json:"maxMessages,omitempty"`
+}
+
+// ServesThreadHistory reports whether the kind answers the op history for threads.
+func (k ConnectorKind) ServesThreadHistory() bool { return k.History != nil && k.History.Thread }
+
+// HistoryLimit is how many messages the host asks for at most: the limit it
+// wants (zero: DefaultHistoryMessages), cut to what the kind declares.
+func (k ConnectorKind) HistoryLimit(want int) int {
+	if want <= 0 || want > MaxHistoryMessages {
+		want = DefaultHistoryMessages
+	}
+	if k.History != nil && k.History.MaxMessages > 0 && k.History.MaxMessages < want {
+		want = k.History.MaxMessages
+	}
+	return want
 }
 
 // ConnectorCapability is the manifest field capabilities.connector.
@@ -121,7 +166,7 @@ type ConnectorCapability struct {
 	Kinds []ConnectorKind `json:"kinds"`
 }
 
-func validateConnector(c *ConnectorCapability, ui *UI) error {
+func validateConnector(c *ConnectorCapability, ui *UI, api VersionRange) error {
 	if c == nil {
 		return nil
 	}
@@ -143,6 +188,14 @@ func validateConnector(c *ConnectorCapability, ui *UI) error {
 		if k.PreviewMs != 0 && (k.PreviewMs < MinPreviewMs || k.PreviewMs > MaxPreviewMs) {
 			return fmt.Errorf("connector previewMs must be 0 or %d to %d", MinPreviewMs, MaxPreviewMs)
 		}
+		if h := k.History; h != nil {
+			if api.Max < MinHistoryAPI {
+				return fmt.Errorf("connector history needs api %d", MinHistoryAPI)
+			}
+			if !h.Thread || h.MaxMessages < 0 || h.MaxMessages > MaxHistoryMessages {
+				return fmt.Errorf("connector history needs thread and maxMessages 0 to %d", MaxHistoryMessages)
+			}
+		}
 		if k.Page != "" {
 			ok := false
 			if ui != nil {
@@ -232,6 +285,12 @@ type ConnectorRequest struct {
 	DraftID int64 `json:"draftId,omitempty"`
 	// media: one reference of ConnectorMessage.Media.
 	Media string `json:"media,omitempty"`
+	// history: Chat and Thread name the thread. Limit is the most messages to
+	// return (1 to MaxHistoryMessages): the newest ones before Before. Before
+	// is the ID of the message that the host handles now; it and the later
+	// messages are not returned.
+	Limit  int    `json:"limit,omitempty"`
+	Before string `json:"before,omitempty"`
 	// send_file: the file. Its name is SafeFileName of itself and its data
 	// is 1 to MaxConnectorFileBytes long.
 	File *ConnectorFile `json:"file,omitempty"`
@@ -268,6 +327,29 @@ type ConnectorResponse struct {
 	BotUsername string `json:"botUsername,omitempty"`
 	// media
 	File *ConnectorFile `json:"file,omitempty"`
+	// history: the messages, oldest first, at most the Limit asked for.
+	// Truncated says that older messages exist that are not returned.
+	Messages  []ConnectorHistoryMessage `json:"messages,omitempty"`
+	Truncated bool                      `json:"truncated,omitempty"`
+}
+
+// ConnectorHistoryMessage is one earlier message of a thread. The text is
+// what other people wrote: the host treats it as untrusted content.
+type ConnectorHistoryMessage struct {
+	MessageID      string `json:"messageId,omitempty"`
+	SenderID       string `json:"senderId,omitempty"`
+	SenderName     string `json:"senderName,omitempty"`
+	SenderUsername string `json:"senderUsername,omitempty"`
+	Text           string `json:"text,omitempty"`
+	// TS is the time of the message, when the platform tells it.
+	TS time.Time `json:"ts,omitzero"`
+	// Own is true for a message of the bot itself.
+	Own bool `json:"own,omitempty"`
+	// Media is how many files the message carries; MediaNames names them
+	// when the platform does, at most MaxHistoryMedia. The bytes are never
+	// part of a history.
+	Media      int      `json:"media,omitempty"`
+	MediaNames []string `json:"mediaNames,omitempty"`
 }
 
 // ConnectorRuntime is a runtime that serves the connector route. An add-on
diff --git a/pkg/addons/contract/connector_test.go b/pkg/addons/contract/connector_test.go
index 5de4e50b9a..41f70636fc 100644
--- a/pkg/addons/contract/connector_test.go
+++ b/pkg/addons/contract/connector_test.go
@@ -42,6 +42,39 @@ var _ = Describe("the connector capability", func() {
 		m.Capabilities.Connector.Kinds[0].Page = ""
 		Expect(ValidateManifest(m, host())).To(Succeed())
 	})
+	Describe("the history ability", func() {
+		kind := func() *ConnectorKind { return &m.Capabilities.Connector.Kinds[0] }
+		BeforeEach(func() { m.API = VersionRange{Min: 1, Max: 2} })
+
+		It("accepts a thread history with the manifest api 2", func() {
+			kind().History = &ConnectorHistory{Thread: true, MaxMessages: 50}
+			Expect(ValidateManifest(m, host())).To(Succeed())
+			Expect(kind().ServesThreadHistory()).To(BeTrue())
+		})
+		It("refuses it under the manifest api 1", func() {
+			m.API = VersionRange{Min: 1, Max: 1}
+			kind().History = &ConnectorHistory{Thread: true}
+			Expect(ValidateManifest(m, host())).NotTo(Succeed())
+		})
+		It("refuses an ability that says nothing and a limit out of bounds", func() {
+			kind().History = &ConnectorHistory{}
+			Expect(ValidateManifest(m, host())).NotTo(Succeed())
+			kind().History = &ConnectorHistory{Thread: true, MaxMessages: MaxHistoryMessages + 1}
+			Expect(ValidateManifest(m, host())).NotTo(Succeed())
+			kind().History = &ConnectorHistory{Thread: true, MaxMessages: -1}
+			Expect(ValidateManifest(m, host())).NotTo(Succeed())
+		})
+		It("serves nothing for a kind that declares nothing", func() {
+			Expect(kind().ServesThreadHistory()).To(BeFalse())
+		})
+		It("cuts the limit to what the kind declares", func() {
+			k := ConnectorKind{History: &ConnectorHistory{Thread: true, MaxMessages: 10}}
+			Expect(k.HistoryLimit(0)).To(Equal(10))
+			Expect(k.HistoryLimit(5)).To(Equal(5))
+			Expect(k.HistoryLimit(500)).To(Equal(10))
+			Expect(ConnectorKind{History: &ConnectorHistory{Thread: true}}.HistoryLimit(0)).To(Equal(DefaultHistoryMessages))
+		})
+	})
 	DescribeTable("refuses",
 		func(edit func(*ConnectorCapability)) {
 			edit(m.Capabilities.Connector)
diff --git a/pkg/addons/contract/manifest.go b/pkg/addons/contract/manifest.go
index e15ea3deaf..0a7431d4c7 100644
--- a/pkg/addons/contract/manifest.go
+++ b/pkg/addons/contract/manifest.go
@@ -403,7 +403,7 @@ func ValidateManifest(m Manifest, h HostCompatibility) error {
 	if e := validateResourceList(c, m.API); e != nil {
 		return e
 	}
-	if e := validateConnector(c.Connector, c.UI); e != nil {
+	if e := validateConnector(c.Connector, c.UI, m.API); e != nil {
 		return e
 	}
 	if e := validateSkillDefinitions(m.ID, c.SkillDefinitions); e != nil {