diff --git a/simplex-chat.cabal b/simplex-chat.cabal
index bd3ca6e353..24ccf24ded 100644
--- a/simplex-chat.cabal
+++ b/simplex-chat.cabal
@@ -84,6 +84,7 @@ library
       Simplex.Chat.Store.Shared
       Simplex.Chat.Styled
       Simplex.Chat.Types
+      Simplex.Chat.Types.MemberRelations
       Simplex.Chat.Types.Preferences
       Simplex.Chat.Types.Shared
       Simplex.Chat.Types.UITheme
@@ -544,6 +545,7 @@ test-suite simplex-chat-test
       JSONFixtures
       JSONTests
       MarkdownTests
+      MemberRelationsTests
       MessageBatching
       OperatorTests
       ProtocolTests
diff --git a/src/Simplex/Chat/Types/MemberRelations.hs b/src/Simplex/Chat/Types/MemberRelations.hs
new file mode 100644
index 0000000000..7245b22472
--- /dev/null
+++ b/src/Simplex/Chat/Types/MemberRelations.hs
@@ -0,0 +1,74 @@
+{-# LANGUAGE LambdaCase #-}
+
+module Simplex.Chat.Types.MemberRelations
+  ( MemberRelation (..),
+    getRelation,
+    setRelation,
+    setRelations,
+  )
+where
+
+import Control.Monad
+import Data.Bits ((.&.), (.|.), complement)
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as B
+import Data.ByteString.Internal (toForeignPtr, unsafeCreate)
+import Data.Int (Int64)
+import Data.Word (Word8)
+import Foreign.ForeignPtr (withForeignPtr)
+import Foreign.Marshal.Utils (copyBytes, fillBytes)
+import Foreign.Ptr (plusPtr)
+import Foreign.Storable (peekByteOff, pokeByteOff)
+
+data MemberRelation
+  = MRNew
+  | MRIntroduced
+  | MRConnected
+  deriving (Eq, Show)
+
+toRelationInt :: MemberRelation -> Word8
+toRelationInt = \case
+  MRNew -> 0
+  MRIntroduced -> 1
+  MRConnected -> 2
+
+fromRelationInt :: Word8 -> MemberRelation
+fromRelationInt = \case
+  0 -> MRNew
+  1 -> MRIntroduced
+  2 -> MRConnected
+  _ -> MRNew
+
+-- | Get the relation status of a member at a given index from the relations vector.
+-- Returns 'MRNew' if the vector is not long enough (lazy initialization).
+getRelation :: Int64 -> ByteString -> MemberRelation
+getRelation i v
+  | i < 0 || fromIntegral i >= B.length v = MRNew
+  | otherwise = fromRelationInt $ (v `B.index` fromIntegral i) .&. relationMask
+
+
+-- | Set the relation status of a member at a given index in the relations vector.
+-- Expands the vector lazily if needed (padding with zeros for 'MRNew' relation).
+setRelation :: Int64 -> MemberRelation -> ByteString -> ByteString
+setRelation i r v
+  | i >= 0 = setRelations [(i, r)] v
+  | otherwise = v
+
+-- | Set multiple relations at once.
+-- Expands the vector lazily if needed (padding with zeros for 'MRNew' relation).
+setRelations :: [(Int64, MemberRelation)] -> ByteString -> ByteString
+setRelations [] v = v
+setRelations relations v =
+  let (fp, off, len) = toForeignPtr v
+      newLen = max len $ fromIntegral $ maximum (map fst relations) + 1
+   in unsafeCreate newLen $ \ptr -> do
+        withForeignPtr fp $ \vPtr -> copyBytes ptr (vPtr `plusPtr` off) len
+        when (newLen > len) $ fillBytes (ptr `plusPtr` len) 0 (newLen - len)
+        forM_ relations $ \(ix, r) -> when (ix >= 0) $ do
+          let i = fromIntegral ix
+          b <- peekByteOff ptr i
+          let b' = (b .&. complement relationMask) .|. toRelationInt r
+          pokeByteOff ptr i b'
+
+relationMask :: Word8
+relationMask = 0x07 -- reserving 3 bits
diff --git a/tests/MemberRelationsTests.hs b/tests/MemberRelationsTests.hs
new file mode 100644
index 0000000000..968dcbec43
--- /dev/null
+++ b/tests/MemberRelationsTests.hs
@@ -0,0 +1,209 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module MemberRelationsTests where
+
+import Control.Monad
+import qualified Data.ByteString as B
+import Simplex.Chat.Types.MemberRelations
+import Test.Hspec
+
+memberRelationsTests :: Spec
+memberRelationsTests = do
+  describe "MemberRelation vector operations" $ do
+    describe "getRelation" $ do
+      it "returns MRNew for empty vector" $ do
+        getRelation 0 B.empty `shouldBe` MRNew
+        getRelation 5 B.empty `shouldBe` MRNew
+        getRelation 100 B.empty `shouldBe` MRNew
+
+      it "returns MRNew for negative index" $ do
+        getRelation (-1) B.empty `shouldBe` MRNew
+        getRelation (-5) (B.pack [0xFF]) `shouldBe` MRNew
+
+      it "returns MRNew for index beyond vector length" $ do
+        let vec = B.pack [0x00]
+        getRelation 10 vec `shouldBe` MRNew
+
+      it "reads single relation from byte" $ do
+        let vec = B.pack [0x01]
+        getRelation 0 vec `shouldBe` MRIntroduced
+
+      it "reads multiple relations" $ do
+        let vec = B.pack [0, 0, 1, 2]
+        getRelation 0 vec `shouldBe` MRNew
+        getRelation 1 vec `shouldBe` MRNew
+        getRelation 2 vec `shouldBe` MRIntroduced
+        getRelation 3 vec `shouldBe` MRConnected
+
+      it "reads multiple relations 2" $ do
+        let vec = B.pack [1, 1, 0, 0, 2, 2, 0, 0]
+        getRelation 0 vec `shouldBe` MRIntroduced
+        getRelation 1 vec `shouldBe` MRIntroduced
+        getRelation 4 vec `shouldBe` MRConnected
+        getRelation 5 vec `shouldBe` MRConnected
+
+      it "ignore reserved bits" $ do
+        let vec = B.pack [0xF9] -- 11111001
+        getRelation 0 vec `shouldBe` MRIntroduced
+
+    describe "setRelation" $ do
+      it "sets relation in empty vector (lazy expansion)" $ do
+        let vec = setRelation 0 MRIntroduced B.empty
+        getRelation 0 vec `shouldBe` MRIntroduced
+
+      it "ignores negative index" $ do
+        let vec = setRelation (-1) MRIntroduced B.empty
+        vec `shouldBe` B.empty
+
+      it "expands vector to required length" $ do
+        let vec = setRelation 5 MRConnected B.empty
+        B.length vec `shouldBe` 6
+        getRelation 5 vec `shouldBe` MRConnected
+        -- Other positions should be MRNew (0)
+        getRelation 0 vec `shouldBe` MRNew
+        getRelation 10 vec `shouldBe` MRNew
+        B.length vec `shouldBe` 6
+
+      it "updates existing relation without affecting others" $ do
+        -- Start: [01][01][00][00]
+        let vec1 = setRelation 0 MRIntroduced B.empty
+        let vec2 = setRelation 1 MRIntroduced vec1
+        -- Update: [01][10][00][00]
+        let vec3 = setRelation 1 MRConnected vec2
+        getRelation 0 vec3 `shouldBe` MRIntroduced
+        getRelation 1 vec3 `shouldBe` MRConnected
+
+      it "updates relation in specific byte of multi-byte vector" $ do
+        let vec1 = setRelation 0 MRIntroduced B.empty
+        let vec2 = setRelation 10 MRConnected vec1
+        B.length vec2 `shouldBe` 11
+        getRelation 0 vec2 `shouldBe` MRIntroduced
+        getRelation 10 vec2 `shouldBe` MRConnected
+        forM_ [1..9] $ \i -> getRelation i vec2 `shouldBe` MRNew
+
+      it "handles setting relation at last position in byte" $ do
+        let vec = setRelation 3 MRConnected B.empty
+        getRelation 3 vec `shouldBe` MRConnected
+
+      it "preserves vector when setting same value" $ do
+        let vec1 = setRelation 0 MRIntroduced B.empty
+        let vec2 = setRelation 0 MRIntroduced vec1
+        vec2 `shouldBe` vec1
+        getRelation 0 vec2 `shouldBe` MRIntroduced
+
+      it "preserves reserved bits" $ do
+        let v = B.pack [0xF8] -- 11111000
+        getRelation 0 v `shouldBe` MRNew
+        let v' = setRelation 0 MRIntroduced v
+        getRelation 0 v' `shouldBe` MRIntroduced
+        B.unpack v' `shouldBe` [0xF9] -- 11111001
+
+    describe "setRelations" $ do
+      it "returns same vector for empty list" $ do
+        let vec = B.pack [0x42]
+        setRelations [] vec `shouldBe` vec
+
+      it "sets multiple relations in empty vector" $ do
+        let updates = [(0, MRIntroduced), (1, MRConnected), (2, MRIntroduced)]
+        let vec = setRelations updates B.empty
+        getRelation 0 vec `shouldBe` MRIntroduced
+        getRelation 1 vec `shouldBe` MRConnected
+        getRelation 2 vec `shouldBe` MRIntroduced
+        getRelation 3 vec `shouldBe` MRNew -- Unset position
+
+      it "sets multiple relations 1" $ do
+        let updates = [(0, MRIntroduced), (1, MRConnected), (2, MRConnected), (3, MRIntroduced)]
+        let vec = setRelations updates B.empty
+        B.length vec `shouldBe` 4
+        getRelation 0 vec `shouldBe` MRIntroduced
+        getRelation 1 vec `shouldBe` MRConnected
+        getRelation 2 vec `shouldBe` MRConnected
+        getRelation 3 vec `shouldBe` MRIntroduced
+
+      it "sets multiple relations 2" $ do
+        let updates = [(0, MRIntroduced), (5, MRConnected), (10, MRIntroduced)]
+        let vec = setRelations updates B.empty
+        B.length vec `shouldBe` 11
+        getRelation 0 vec `shouldBe` MRIntroduced
+        getRelation 5 vec `shouldBe` MRConnected
+        getRelation 10 vec `shouldBe` MRIntroduced
+        getRelation 7 vec `shouldBe` MRNew -- Unset position between
+
+      it "handles sparse updates (few indices in large range)" $ do
+        -- Sparse: 3 updates in large group
+        let updates = [(0, MRIntroduced), (100, MRConnected), (5000, MRIntroduced)]
+        let vec = setRelations updates B.empty
+        getRelation 0 vec `shouldBe` MRIntroduced
+        getRelation 100 vec `shouldBe` MRConnected
+        getRelation 5000 vec `shouldBe` MRIntroduced
+        getRelation 50 vec `shouldBe` MRNew -- Untouched position
+
+      it "handles dense updates (many consecutive indices)" $ do
+        -- Dense: many consecutive updates
+        let updates = [(i, if even i then MRIntroduced else MRConnected) | i <- [0 .. 99]]
+        let vec = setRelations updates B.empty
+        all (\i -> getRelation i vec == (if even i then MRIntroduced else MRConnected)) [0 .. 99] `shouldBe` True
+
+      it "handles unsorted input correctly" $ do
+        let updates = [(10, MRConnected), (2, MRIntroduced), (5, MRConnected), (0, MRIntroduced)]
+        let vec = setRelations updates B.empty
+        getRelation 0 vec `shouldBe` MRIntroduced
+        getRelation 2 vec `shouldBe` MRIntroduced
+        getRelation 5 vec `shouldBe` MRConnected
+        getRelation 10 vec `shouldBe` MRConnected
+
+      it "handles duplicate indices (last one wins)" $ do
+        let updates = [(0, MRIntroduced), (0, MRConnected), (0, MRIntroduced)]
+        let vec = setRelations updates B.empty
+        getRelation 0 vec `shouldBe` MRIntroduced
+
+      it "preserves existing relations not in update list" $ do
+        let vec1 = setRelation 0 MRConnected B.empty
+        let vec2 = setRelation 5 MRIntroduced vec1
+        let updates = [(10, MRConnected)]
+        let vec3 = setRelations updates vec2
+        getRelation 0 vec3 `shouldBe` MRConnected
+        getRelation 5 vec3 `shouldBe` MRIntroduced
+        getRelation 10 vec3 `shouldBe` MRConnected
+
+    describe "edge cases and invariants" $ do
+      it "round-trip: set then get returns same value" $ do
+        let vec1 = setRelation 42 MRConnected B.empty
+        getRelation 42 vec1 `shouldBe` MRConnected
+
+      it "multiple round-trips preserve values" $ do
+        let vec1 = setRelation 0 MRIntroduced B.empty
+        let vec2 = setRelation 1 MRConnected vec1
+        let vec3 = setRelation 2 MRIntroduced vec2
+        getRelation 0 vec3 `shouldBe` MRIntroduced
+        getRelation 1 vec3 `shouldBe` MRConnected
+        getRelation 2 vec3 `shouldBe` MRIntroduced
+
+      it "setRelations equivalent to multiple setRelation calls" $ do
+        let updates = [(0, MRIntroduced), (5, MRConnected), (10, MRIntroduced)]
+        let vecBatch = setRelations updates B.empty
+        let vecSeq = setRelation 10 MRIntroduced $ setRelation 5 MRConnected $ setRelation 0 MRIntroduced B.empty
+        vecBatch `shouldBe` vecSeq
+        getRelation 0 vecBatch `shouldBe` getRelation 0 vecSeq
+        getRelation 5 vecBatch `shouldBe` getRelation 5 vecSeq
+        getRelation 10 vecBatch `shouldBe` getRelation 10 vecSeq
+
+      it "handles large group size (10000 members)" $ do
+        let updates = [(0, MRIntroduced), (5000, MRConnected), (9999, MRIntroduced)]
+        let vec = setRelations updates B.empty
+        B.length vec `shouldBe` 10000
+        getRelation 0 vec `shouldBe` MRIntroduced
+        getRelation 5000 vec `shouldBe` MRConnected
+        getRelation 9999 vec `shouldBe` MRIntroduced
+
+      it "all status values can be stored and retrieved" $ do
+        let vec1 = setRelation 0 MRNew B.empty
+        let vec2 = setRelation 1 MRIntroduced vec1
+        let vec3 = setRelation 2 MRConnected vec2
+        getRelation 0 vec3 `shouldBe` MRNew
+        getRelation 1 vec3 `shouldBe` MRIntroduced
+        getRelation 2 vec3 `shouldBe` MRConnected
+
+      it "vector length is minimal (lazy expansion)" $ do
+        let vec = setRelation 3 MRConnected B.empty
+        B.length vec `shouldBe` 4
diff --git a/tests/Test.hs b/tests/Test.hs
index e4e76fd43e..e1a5a58c7d 100644
--- a/tests/Test.hs
+++ b/tests/Test.hs
@@ -13,6 +13,7 @@ import Control.Logger.Simple
 import Data.Time.Clock.System
 import JSONTests
 import MarkdownTests
+import MemberRelationsTests
 import MessageBatching
 import ProtocolTests
 import OperatorTests
@@ -59,6 +60,7 @@ main = do
 #endif
       describe "SimpleX chat markdown" markdownTests
       describe "JSON Tests" jsonTests
+      describe "Member relations" memberRelationsTests
       describe "SimpleX chat view" viewTests
       describe "SimpleX chat protocol" protocolTests
       describe "Valid names" validNameTests